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Suborbital refuelling

steelpillow

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There has been mention elsewhere of suborbital refueling as a way to get a practical spaceplane into orbit.

I am baffled as to any benefit over having the tanker and orbiter strapped together as a two-stage or composite spaceplane until the orbiter is released with its full fuel load. Can anybody explain?
 

Archibald

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Not at home presently. Tonight I will post a whole bunch of documents from M.B. Clapp, A. Goff and my own little contribution to the matter.
By the way if anybody knows Jeff Foust from The Space Review... I need to be coopted to publish there... any help would be welcome.

Waiting for that...

Bimese and Trimese, if identical vehicles, end very suboptimal and inefficient. Booster is no orbiter, orbiter cannot be a booster. This killed GD Triamese back in the day, april 1969 when they pitched it to NASA for shuttle.
As for different vehicles mated together - as per early shuttle studies, 1969-71 - they are different vehicles (d'oh !) with separate development costs... and expensive.

You can think also as a SSTO-helper. Basically instead of building a daunting Venture Star with an impossible mass fraction (0.92), build a couple of suborbital X-33s with a far lower mass fraction of 0.80 and achieve SSTO with a small LOX transfer between these two vehicles.
The tanker can really be identical, think not KC-135 but buddy-buddy refueling, USN style.

 
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martinbayer

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Not at home presently. Tonight I will post a whole bunch of documents from M.B. Clapp, A. Goff and my own little contribution to the matter.
By the way if anybody knows Jeff Foust from The Space Review... I need to be coopted to publish there... any help would be welcome.

Waiting for that...

Bimese and Trimese, if identical vehicles, end very suboptimal and inefficient. Booster is no orbiter, orbiter cannot be a booster. This killed GD Triamese back in the day, april 1969 when they pitched it to NASA for shuttle.
As for different vehicles mated together - as per early shuttle studies, 1969-71 - they are different vehicles (d'oh !) with separate development costs... and expensive.

You can think also as a SSTO-helper. Basically instead of building a daunting Venture Star with an impossible mass fraction (0.92), build a couple of suborbital X-33s with a far lower mass fraction of 0.80 and achieve SSTO with a small LOX transfer between these two vehicles.
The tanker can really be identical, think not KC-135 but buddy-buddy refueling, USN style.

Archibald, things are by far not as black and white as you make them seem - there are 2STO (or potentially even 3STO - think son of MUSTARD) concepts that have some commonality across stages without being completely identical. Over two decades ago I was involved in ESA's Future European Space Transportation Investigations Programme (FESTIP) System Studies, see https://www.esa.int/esapub/bulletin/bullet97/dujarric.pdf, where the concept analysis and evolution of a VTHL TSTO RLV eventually led to an 'almost' bimese configuration called Festip System Studies Concept (FSSC) 16, see http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=30547.0;attach=536078 (note that while I authored the paper, someone else unbeknownst to me obtained a copy and released it on the web without consent). The development cost of this configuration was found to be the lowest of all fully reusable FESTIP concepts comprising various SSTO and TSTO designs developed to the same requirements and reference missions - far from being "very suboptimal and inefficient" while also reducing ops costs over a "classical" TSTO RLV.

Suborbital refueling on the other hand requires not only two separate vehicles but also two separate sets of launch infrastructure and operations teams to achieve the same mission while adding a time critical rendezvous maneuver during ascent that (if I understand correctly) necessitates two additional potentially significant risk events, i.e. in flight vehicle coupling as well as termination and subsequent reignition of the orbiter main propulsion system, that are not present in a parallel burn TSTO with continuous crossfeed. Those additional risk factors alone raise major red flags in my view. Add to that the additional gravity losses incurred during the free fall propellant transfer, and I don't see how this would ever be an attractive solution for routine commercial space transportation (imagine a captain's voice over the intercom after liftoff reassuringly telling a cabinload of space tourists: "Ladies and Gentleman, before going to orbit we have to get a quick top off on the fly to make sure we can make it all the way up, but don't worry, based on long term experience we only have to abort due to any associated issues in about every fiftieth flight..."

Martin
 
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Archibald

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Total respect about your credentials and experience, M. Bayer. As such, I agree over you demolishing my suboptimal bimese / trimese arguments. It was based on the 1968 GD design. Note I won't use it anymore (and remove that argument from the papers ASAP).

- I have that Dujarric paper, I red it. I personally had a crush for the FSSC-15, the suborbital hopper. What a clever concept that was, launch from Europe, drop an expendable upper stage, land in Kourou. And cheap with that.

- No need for two launch complexes / gantries if the two vehicles are HTOHL. Just get a pair of turbofans plus a rocket. Liftoff from an air base or an airport.

VERSATILITY
Such a rocketplane, even without suborbital refueling, could do the following missions
- SS2 / New Shepard suborbital tourism
- P2P ballistic passenger transportation (ricochet trajectories, see Preston H. Carter Hypersoar work)
- satellite launch with an expendable upper stage (think Rocketplane Pathfinder and KST Astroliner from the 90's).
- And with the addition of a twin vehicle configured as a buddy-buddy tanker, it can goes into orbit.

- Your other red flag: if the rocketplane burns hydrogen peroxide with kerosene, the O/F ratio is 7 to 1. Which mean only peroxide is transfered. And since it is non-cryogenic, you can do that USN style - probe, drogue, and bladder. It is not me who noted that but Mitchell Burnside Clapp.

LOX by contrast is much harder, being a mild-deep cryogen. It needs a more rigid system. Boom rendezvous might be the answer.
LOX/LH2 has an O/F ratio of 5 - 6 and keep that advantage, except with a far, far better specific impulse that greatly helps payload to orbit. No way to transfer LH2 in flight, that would be insane. Only LOX.

Note that for kerolox and methalox, O/F ratio of only 2 - 3 mean fuel would have to be transfered along with oxidizer, and that would make the prop transfer trickier, two fluids is too much.


Gravity losses have been considered in the papers I send you in private. I link them again here.

--------------

But there is more... the FLOC effect. The refueling is not only useful to get a quasi-SSTO in orbit more easily. It also has a profound effect on the payload to orbit. Two, three, four vehicle FLOC raise payload to orbit. At the expense of a complex suborbital ballet, admittedly.

I link four papers dealing with Alan Goff research - two from him and two independant critics. What he and Mitchell Burnside Clapp found independantly (in 1995 and 2004, respectively) is the massively positive effect on payload.

I also link an excerpt from Clapp and Zubrin 1995 Analog paper. Where Clapp briefly discuss suborbital refueling.
 

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martinbayer

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Hello Archibald,

no need to get formal and address me as "M. Bayer" - just call me Martin, but I'm good either way, just as long as you don't start using "Mr." or "Sir", because then I usually know I'm in trouble :).

To me the Hopper was always a dead end niche concept that might have been a modest stepping stone to introducing partial reusability and associated learning effects and lowering pure launch cost for smaller payloads, but in my view only true and *full* reusability will allow to not just deploy but also routinely retrieve and return payloads and thus open up a whole new set of missions and orbital activities - something FSSC-16 would have supported at least to some extent, so the comparison is really apples vs. oranges. Based on your statements above, I can now see though that you likely looked at it as yet another potential avenue to the concept under discussion here.

You mentioned using the X-33 design, so I assumed you were referring to a VTHL system - apart from the needlessly complex tank shapes that caused the concept's demise, I'm not sure though whether the *fat* lifting body aerodynamics would really be a good fit for an at least somewhat aerodynamic jet powered ascent as compared to a more conventional and slender wing-body configuration like the Teledyne spaceplane or FSSC-16 (or IMHO really for *any* aerodynamic maneuvers, for that matter). Adding jet engines to both vehicles obviously adds complexity and weight for both instead of just the booster in the almost bimese case, and if you used the original X-33 as the point of departure for two *completely* identical but separately launched stages, you would now incur a lot of other similar inefficiencies like a true bimese, e.g. orbital capable TPS and OMS on both stages, having an empty payload bay on the booster, both active and passive refueling equipment on both stages, etc..

Instead of just taking Mitchell Burnside Clapp's breezy assertion that buddy type suborbital refueling is really a lead-pipe cinch at face value, I'd want to see *any* two vehicle rendezvous, linkup, and propellant(s) transfer in coasting ascent per se (irrespective of propellant densities, temperatures, number of propellant components, etc. - for proof of concept you could initially even use water, for all I care) *repeatedly* demonstrated reliably in actual flight and representative environments in principle before I would put *any* practical credence in that concept for routine operational purposes. The risk factors remain, and of course that applies even exponentially more so to the flock concept.

I also note that, at least after cursory perusing of your uploads, none of the papers really provide a detailed, honest to god head to head comparative analysis of a TSTO vs. an aerial hookup system. In fact, for example in the 2006 AIAA paper "Economics of Separated Ascent Stage Launch Vehicles" a footnote on page 8 characterizes an assumed structure mass fraction with admittedly remarkably candid and refreshing honesty explicitly as a "Wild Guess". The closest reference I could find so far to some kind of comparison is on page 4 of the AIAA 2004 paper called "The Flock Booster Architecture – Low Cost Access to LEO via Sustained Fueling", which refers to two winged boosters mated belly to belly for a vertical launch off a standard launch pad. Apart from a basic booster delta v calculation, there are however really no quantitative comparative analyses with two separately vertically launched stages, only the qualitative assertion that "[w]hile vertical launch is possible, the time required to lift and mate the boosters on a launch pad is very costly, and requires both specialized equipment and a dedicated launch pad", whereas apparently (nearly) effortless horizontal launch is automatically assumed for separately launched stages. But even under the assumption of vertical launch for a rocket powered launch vehicle with at least partial reusability, Elon Musk might have a tought or two on the actual time, cost and required equipment to do so ;).

Martin
 
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Archibald

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I consider Musk system to be the equivalent of a Boeing 747 to space. The 747 was the final touch that send passenger transportation into massification and low rates. Before the 747 however were the 737, 707, Constellation, DC-3 and Ju-52. Each one a new step into lowering the cost
- Ju-52 barely allowed companies to earn money
- DC-3 crossed that treshold
- Constellation pushed across the Atlantic but piston engines ran into their limits
- 707 turned the tables with jet engines.
- 747 massified the whole thing on long range flights with large numbers of passengers
- 737 did the same but on short-haul lines

The SOR system is to Musk BFR/BFS what 737 is to 747. Complementary. Smaller and easier to use. More flexible.

-------------------

TSTO vs aerial hookup: with a lot of help (from a person that will recognize himself )- we made Excel spreadsheets.
Here is a volley of screenshots showing some results.

- the better the specific impulse, the smaller the prop transfer.
 

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Archibald

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Instead of just taking Mitchell Burnside Clapp's breezy assertion that buddy type suborbital refueling is really a lead-pipe cinch at face value, I'd want to see *any* two vehicle rendezvous, linkup, and propellant(s) transfer in coasting ascent per se (irrespective of propellant densities, temperatures, number of propellant components, etc. - for proof of concept you could initially even use water, for all I care) *repeatedly* demonstrated reliably in actual flight and representative environments in principle before I would put *any* practical credence in that concept for routine operational purposes. The risk factors remain, and of course that applies even exponentially more so to the flock concept.
Yes, absolutely agree with that statement.

The entire refueling system needs a very thorough flight test program.
To speak like Elon Musk - the keroxide bird is the Mk.1 and the hydrolox is Mk.2.

Step 1
Take an Il-76 cargo plane. Put a big trailer truck full of H2O2 in the cargo hold. Open the doors in flight, and let a probe-and-drogue system unfurl. Have a prototype Mk.1 rocketplane quietly try tanking in subsonic flight.

Step 2
Still in subsonic flight, replace the Il-76 by a second rocketplane with a buddy-buddy pack

Step 3
try that in parabolic flight at 80 000 ft.

Step 4
The big jump: try that in suborbital.

Step 5
Rinse, repeat step 1 to 4 with a new LOX rocketplane, the Mk.2.

Step 6
Also use the older, Mk.1 keroxide rocketplanes. They have a LOX refueling buddy pack in their payload bays.
First try a LOX refueling in a stable Earth orbit. Unlimited time to proceed.
Then try in suborbital flight.
 

Archibald

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the crux of the matter is basically to wrap bits of airliner - wings tail jets cockpit undercarriage - around a rocket stage 1. And to liftoff from an ordinary airstrip on jet power alone.
That combination cannot be wrapped into a SSTO mass fraction, 0.88 for LH2 and 0.95 for other props. Waaaay too heavy.

By relaxing the PMF to 0.85 or even 0.80 for LH2, suborbital refuelings allows to build a SSTO more easily (well call that a failed-SSTO or a quasi-SSTO if you like ).

For example

9.81*327*ln(120/18) = 6100 m/s.
Fails since Earth orbit is 9000 m/s. Not enough props !
So how much more props ?
9.81*327*ln(300/18) = 9000 m/s

300 mt into the same empty mass of 18 mt. As if 120 mt wasn't already pushing the limits !

look at that: going from 0.85 PMF to SSTO 0.95 took a whopping 150% more propellant ! this is because of the freakkin' logarithm stuck in the equation: non linear, exponential.

I vastly prefer deliberately building a failed-SSTO knowing I can and will fill the delta-v gap with one suborbital refueling
THAN
failing miserably like NASA and Lockheed X-33 and VentureStar.
 

steelpillow

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As for different vehicles mated together - as per early shuttle studies, 1969-71 - they are different vehicles (d'oh !) with separate development costs... and expensive.
Surely this also applies to suborbital refueling between specialist tanker and orbiter. Moreover mating together dynamically, whether during a free-fall phase or a joint powered flight phase, hardly sounds cheaper or more efficient than mating together statically before takeoff.

you can do that USN style - probe, drogue, and bladder.
That implies aerial refueling, which is not what I would describe as "sub-orbital". I think we need a bit of clarification here as well.
My old "piggyback" HOTOL (predating the An-22 Mriya project) refueled from the carrier aircraft to replace cryogenic boiloff and had the added advantage of reducing the wing area of the orbiter even more than near-empty tankage would, due to the assisted takeoff.
 
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Archibald

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No the tanker is identical to the orbiter. The amount of oxidizer (20 000 to 100 000 pounds) to be transfered is taken from the tanker internal tanks and passed to the orbiter.

As for USN style - I meant the hardware. Probe drogue bladders. Adapted to suborbital environment of course - space vacuum but no turbulence outside the atmosphere. 50 miles high during a X-15 like ballistic flight. A segment of orbit only since a complete one takes 8 km/s.
 

martinbayer

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Archibald,

as an engineer, I am a big believer in the KISS principle, and performing suborbital trapeze acts is *NOT* part of that. If you want to convince me, show me a *quantitative* comparison (in terms of both mass and cost estimates - I'm not even asking for risk assessments) between a bimese TSTO RLV and your free fall mating concept for the same technology level. Remember, just because something *might* work doesn't automatically mean it's the best solution ever. As an example, I brought up gravity losses during the zero g refueling maneuver, to which you essentially replied they had been calculated. That's nice, but that still means they occur and quite literally constitute a drawback on your concept that a straight up continuous burn parallel staged TSTO doesn't have.

Martin
 
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steelpillow

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No the tanker is identical to the orbiter. The amount of oxidizer (20 000 to 100 000 pounds) to be transfered is taken from the tanker internal tanks and passed to the orbiter.

As for USN style - I meant the hardware. Probe drogue bladders. Adapted to suborbital environment of course - space vacuum but no turbulence outside the atmosphere. 50 miles high during a X-15 like ballistic flight. A segment of orbit only since a complete one takes 8 km/s.
So, you write, "Bimese and Trimese, if identical vehicles, end very suboptimal and inefficient." and then you write, "No the tanker is identical to the orbiter." Can you please explain how a bimese tanker plus identical orbiter would not be bimese? You might like to read up on MUSTARD first, in which multiple non-orbital craft doubled as combined booster/tankers.

Also, for your information a "drogue" is a particular device which relies on aerodynamic or hydrodynamic drag to stabilise itself. The refueling application was developed in the UK and from there became a NATO standard. It has no equivalent in space and any probe impacting the hose would meet no resistance to pushing the hose away from it. The craft would need to lock together directly via a "refueling lock" similar to an airlock. One might deploy a short fuel tube capable of resisting longitudinal compressive forces, but I am not sure there would be much point. I am also puzzled by your reference to bladders. What function to they serve?

Are the craft expected to maintain engine thrust while the fuel transfer is taking place? If yes, that adds a lot of stress to the fuel lock. If no, the time spent in sub-orbital free fall represents a massive waste of the fuel used up to that moment.
 

Archibald

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So, you write, "Bimese and Trimese, if identical vehicles, end very suboptimal and inefficient." and then you write, "No the tanker is identical to the orbiter." Can you please explain how a bimese tanker plus identical orbiter would not be bimese? You might like to read up on MUSTARD first, in which multiple non-orbital craft doubled as combined booster/tankers.
because they are SEPARATED maybe ? as in, not attached to each other ?

Two identical vehicles attached to each other from the ground to orbit drag their respective masses together. If they ascent separated, the masses are separated, too, except for the brief moment when they link for the refueling. And this has a massive effect on payload. Please read the papers I attached up thread.

Are the craft expected to maintain engine thrust while the fuel transfer is taking place? If yes, that adds a lot of stress to the fuel lock. If no, the time spent in sub-orbital free fall represents a massive waste of the fuel used up to that moment.
They throttle down. No, they won't try to hook firing at 100% thrust, it would be suicide.
As for gravity losses, once again, please make the effort of reading all the things I took the pain to download, read, assimilate, and link here.
The refueling last 1 minutes to 5 minute, no more.

Bladders, drogue, probe

Please note that
a) english is not my native language
b) as noted earlier in the thread, I'm using Clapp vocabulary.
c) the refueling system is not 100% detailed so far, I'm using aerial refueling system experience as the closest thing in existence, but admittedly it has to be adapted. I'm all too aware a Cobham refuelng pack build for the atmosphere won't work in space.
d) Present aerial refueling systems are the USAF rigid boom and the USN thing. Yet suborbital refueling may marry them, adapt them, to boom rendez vous I mentionned up thread ( once again).

And Mustard inspired Triamese and both were not workable as discussed up thread. NASA expressedly rejected Triamese for Shuttle as early as april 1969, for these reasons. See Heppenheimer SP-4221 NASA history, 1999. The space shuttle decision.
Only FSSC-16 is a workable design.
 
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martinbayer

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Archibald,

note that the bimese TSTO eventually ends up separated as well, it just doesn't start out that way. All other things being equal, you seem to think that mating two vehicles at rest on the surface of the Earth is tricky, risky, and inefficient, but doing the same quite literally on the fly isn't. I beg to differ. Also, DC-X already showed almost three decades ago that vertical launch of a reusable vehicle really doesn't necessarily have to be any more complicated than horizontal takeoff. In addition, as best as I can tell, *none* of the papers you have provided so far features an *explicit* quantitative comparison of a "classical" TSTO with the celestial hookup concept that would show the "massive effect on payload" you claim above. After having read "Britain's Space Shuttle" by Dan Sharp, who is an esteemed member of this forum, I dare say that a whole lot more competent thought and professional work was put into MUSTARD than into say the flock synchronized launching routine.

Martin
 
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Archibald

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This is an unfair comparison. The studies were not of the same scope ! Alan Goff is not the British government. Common !

Link to Alan Goff profile on Linkedin. https://www.linkedin.com/in/allan-goff/

. As an example, I brought up gravity losses during the zero g refueling maneuver, to which you essentially replied they had been calculated. That's nice, but that still means they occur and quite literally constitute a drawback on your concept that a straight up continuous burn parallel staged TSTO doesn't have.
Are you kidding ? We all know gravity losses are added past 7.8 km/s (with steering and drag losses) and together they add 1.3 km/s, up to 9km/s or more, average. Every launch vehicle suffer from this penalty, your bimese and my system altogether. You still doesn't have red my paper, incidentally. I take into consideration gravity losses, mind you.

The reason why suborbital refueling (or docking, but I don't like docking) is a massive force multiplier is very well explained by Alan goff in his first FLOC paper I linked. And since aparently nobody takes time to read anything before arguing (sigh) I will quote Goff directly

binary staging thereby approximating continuous staging. This yields a launch system with a true fuel scaling law instead of a limit law, and a booster design relatively insensitive to dry mass fraction (in sharp contrast to current launch systems).
The fuel scaling law avoids the limit velocity characteristic of any fixed stage rocket; there is no upper
limit delta-V for Flock. The insensitivity to dry mass fraction enables new engineering tradeoffs that
can favor cost, reliability, safety, flexibility, maintainability, minimal ground crews, fast turnaround times.

Benefits
The primary benefits of Flock are a fuel scaling law that is not a limit law and system performance that is relatively insensitive to the dry mass fraction of the individual boosters. This means that a Flock rocket plane can be designed to life cycle costs instead of performance.
High dry mass fractions offer many new engineering tradeoffs, which can benefit cost, safety, reliability,
maintainability, turnaround times, small ground crews, etc. Since all stages and inter-stage interfaces
are identical, significant economies of scale can be realized as well. Cost per kilogram to orbit should be at least an order of magnitude less than for conventional systems, and payloads can be several times larger too.
I also quote Clapp, a speculative idea

Consider the case where we have two Black Horse type vehicles, each using JP-5/H2O2 with an Isp
of 335 s. The vehicles have a dry weight of 15,000 lb and a propellant load of 180,000 lb, which
assuming a required Delta-v to orbit of 27 kft/s, allows them to deliver 1,000 lb to LEO. Now, let's
say that we fly the two of them off together, accelerating them jointly not to orbit, but rather to a
suborbital trajectory with a velocity of 18.5 kft/ s. The two space planes are now outside the
atmosphere, in free fall (i.e. zero gravity) in the immediate vicinity of each other. Let's say we now
bring the two together and extend a refueling boom, allowing the 20,000 lb of residual propellant
from one to be transferred to the other. The two then separate, the empty vehicle to return to Earth,
the enriched vehicle to ascend to orbit with a payload of 12,000 lbs. Without any new hardware, the
orbital delivery capability of the system can be increased by a factor of 12.
I re-did Clapp calculations through an Excel spreadsheet, and it works. See the attached pictures up thread.
 

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Archibald

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I would like to precise something.

In the paper "A speculative idea" Clapp mentions two rocketplanes, refueling, with a very high PMF (Black Horse was 0.92, Black Colt, 0.80).
In the FLOC concept Goff smallest FLOC has 8 rocketplanes that dock, with far lower PMF of 0.72.

I want to hit right between the two. I consider FLOC is a bridge too far but that Clapp did not pushed his "speculative idea" far enough.

That is, PMF 0.85 and more importantly - more than two birds, but a maximum of eight. I want to explore the 2-FLOC, 3-FLOC, 4-FLOC combinations. Well, even 8-FLOC is kind of bridge too far, the whole thing become unbalanced.

The main interest is really to get 2, 3 or 4 rocketplanes refueling each others. This limit complexity but already maximizes payload.
 

martinbayer

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There is a reason why some concepts are studied significantly more often and in far greater depth than others. "Fairness" has nothing to do with it, it is more based on which ones are deemed promising and which ones aren't. Dismissing one concept that was refined over several years by one of the then preeminent aerospace companies of the world while latching on to another promulgated by some individuals in their spare time does not instill confidence in me.

I'm unsure whether you intentionally misunderstood or misinterpreted me, but while gravity losses are of course incurred by all launch vehicles, coasting phases needlessly add to them and should be avoided or minimized.

If you are willing to entertain ever larger numbers (and potentially sizes) of parallel or series stages, there is no theoretical upper limit delta-v for "classical" staged launch vehicles either.

If you have a spreadsheet set up that allows you to replicate someone else's launch vehicle performance calculations, you should have no problem to determine comparative results for a propellant transfer architecture vs. a "conventional" VTHL TSTO RLV with parallel staging and continuous crossfeed under the same technology assumptions. I look forward to you sharing the concrete results and any associated insights.
 
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steelpillow

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OK, so which of the six linked papers contains the quantitative analysis showing how splitting the launches apart makes such a massive improvement over suborbital separation? I couldn't find any, though I confess that studying all six in detail just to test a seemingly bizarre claim is not something I intend to do.
 

Archibald

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Ok so this thread is over then. Goodbye. Happy with the results ? You did not gave the idea a chance. I let you both enjoying your victory.

Your attitude is pathetic, really. I gave you the keys to try and understand the concept, and you refuse these keys. Well, what's the point in arguing with a pair of bricks ?
 

martinbayer

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Oh, I understand the concept, I'm just waiting for you to provide comparative analytical evidence for its purported superiority. Is that too much to ask?
 
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steelpillow

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Steelpillow, I completely concur with your analysis and conclusion.
Thank you.

So I had an idle moment, found Goff's paper and read at least some of it:
  • He notes thet the cost of step-rockets has not changed hugely over the years. He compares this intuitively with re-usable spaceplanes, without taking into account the benefits of re-usability for step rockets. These are now being realised by companies such as SpaceX.
  • His flock of 2^n refuelling tankers reminds me of the UK Vulcan bombing raids on the Falkland islands. The RAF were crystal clear that the multiple refuelling logistics were an utter nightmare and nearly put paid to the whole exercise. For a start you have 2^n times as many things to go wrong. It is a rather obvious thing that a twin-engined airliner is less likely to have an engine failure than a four-engined type so, since two engines became feasible, the four-engined types have begun dying out. I see no reason for operating economics to differ in space. Especially when there are no numbers to back the theory up.
  • Here is the sum total of his claimed "analysis" that two separate launches are more efficient: "While vertical launch is possible, the time required to lift and mate the boosters on a launch pad is very costly, and requires both specialized equipment and a dedicated launch pad. Alternatively, consider two simultaneous horizontal launches, followed by a sustained fueling maneuver in the lower atmosphere right after
  • takeoff." Not a number in sight. Note however the atmospheric in-flight refuelling "right after takeoff". And he compares vertical against horizontal as if these were intrinsic to each case. Where are the two independent vertical launches or the single composite spaceplane takeoff? This is worthless speculation.
One of the other papers waxed lyrical on the possibilities of refuelling in low Earth orbit. Arthur C Clarke remarked back in 1947 that once you reach low Earth orbit you are halfway to anywhere [in the Universe]. It takes just half of the Earth's escape energy budget to reach LEO. Given a single top-up to reach LEO, you need two more to make it to interstellar space. Old news, but there you go.

Sorry, my idle moment just ended.
 

steelpillow

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Ok so this thread is over then. Goodbye. Happy with the results ? You did not gave the idea a chance. I let you both enjoying your victory.

Your attitude is pathetic, really. I gave you the keys to try and understand the concept, and you refuse these keys. Well, what's the point in arguing with a pair of bricks ?
We gave you every chance. It was the whole reason I opened this thread. Do not kid yourself you are important enough for me to waste my life opening it just so i could diss you. I really wanted to know more, which you did post and I thank you for that.
But when it came to convincing rocket science, you blew it. Not your fault, the economics do not stack up, the evidence to support those wild claims is just not there (see my comments on Goff above). But just cool down a bit, and you may yet learn something useful.

I do think that it is technically feasible, just as the Vulcan missions were. But like them I also see it as a last resort. Maybe where the design performance of an existing system needed extending. And it would be and option to explore only when neither atmospheric nor LEO refuelling was available for some reason. Maybe one day this discussion will light up again, who knows.
 
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RanulfC

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Flyby-Posting-Excursion-Mode...(Hey at least it's not as bad as "FLEM" :) )
Background: 21 years Air Force maintenance and support, explosives training, (more C4 always solves the problem as long as you ignore the collateral damage) electronics and airframe maintenance. 6 years cruise missile mainteance and ICBM support systems maintenance and a LOT of reading, internet searching and questioning experts.

I'll point out that I'd meant to advice Archibald that in fact you can NOT use the 'droge-n-probe' system for a varity of reasons and the system would more resemble, (but would not be) the boom style system. However out communications didn't mesh and likely my response to him is still sitting in my currently non-op laptop. Apperantly this also included my discussion of the propellant transfer system so he's still using the incorrect "Air To Air" (A2) systems as a place holder. I'll explain that below but it's not really as 'far out' as it might seem though the use of current A2A systems as analogs makes it hard to swallow. So while I'm not wedded to the concept I also don't feel it is a non-viable concept either.

This was studied pretty extensivly under the 1950s/60s "Aerospaceplane" project and before they switched to in-flight liquid oxygen production was the front-running contender. (At Mach 6, in the atmosphere no less) Needless to say the expression most often used to show how 'easy' THAT idea was went something like "It's JUST engineering" :) The heating issues and difficulty of 'hooking up' at that speed were rather obvious, so the rendzvous was moved outside the effective atmosphere still at the same speed. Planning went as far as considering using two X-15s flying in close formation to 'test' the idea. We didn't HAVE two X-15 at that point in time and by the time we did the program had moved on but...

Now having gotten that out of the way let me try and address some of the questions that I've seen:
There has been mention elsewhere of suborbital refueling as a way to get a practical spaceplane into orbit.

I am baffled as to any benefit over having the tanker and orbiter strapped together as a two-stage or composite spaceplane until the orbiter is released with its full fuel load. Can anybody explain?
In essence the concept is an 'assisted' SSTO using two near-SSTO's and propellant transfer instead of a dedicated booster and orbiter. (Everything is an orbiter) In the cited early Bi/Trimese studies the use of orbiters as boosters was a major efficiency issue (and this is still true today) because the 'booster' now had mass and complexity it didn't need even though in 'theory' it could be used as an orbiter as well. In truth, and especially as most studies used LH2, trying to pack the 'booster' propellant in the payload bay didn't work so you ended up with having to have a dedicated "booster" and orbiter airframe with all the design and development costs therein. As cost scales with airframe size in aerospace a set of smaller airframes is going to be less costly than a single large one. (Operationally it can be argued they'd come in at a lower overall cost as well)

So the use of dense H2O2 and kerosene is an advantage as you can actually "fit" it into a notional "buddy pack" in the cargo bay.

Operationally if the notional TSTO fires all engines on launch and has propellant cross-feed to seperation then the analogy works but that has its own issues to deal with. (Exhaust plume interaction and aerodynamic and hydraluic stress' for example) In this case the vehicles are only in close proximity for a short period of time under almost free-fall conditions in a vacuum. While here you have both a rendezvous and seperation event that may actually be both easier and less complex than ground mating and suborbital seperation of the mated vehicles as you avoid the interconnection gear and aerodynamic systems required to make the TSTO work. The mass and complexity of the rendezvous and tanking gear is of course non-trivial but at the same time you already HAVE the rendzvous gear since you need it on-orbit anyway and the propellant transfer system can be pretty light weight.

Your abort options are greater since you don't have to worry about seperating a mated pair of vehicles should something go wrong. As they say the devil is in the details and the details are themselve greatly dependent on a number of choices along the design path but in essence I would sum it up as the same basic benifits that you get by having seperate tankers and aircraft rather than mounting F-35s on top of KC-135 to transport them half way to Europe before sending them on their way :)

Horrible analogy but somewhat apt.

Arthur C Clarke remarked back in 1947 that once you reach low Earth orbit you are halfway to anywhere [in the Universe].
AhhhHEM there mister, want to correct that before Bob comes down from heaven and set you straight? :)

Martin, something to keep in mind when evaluating concepts such as this is they more resemble aircraft rather than space launch operations which as we know is the 'Holy Grail' of space launch. In theory anyway :)

Your launch operations consist of a ground crew, supply and support systems and a big, long flat stretch of flatness. Not a launch trench, exhaust deflector, water suppression system, launch tower, need I go on? Now it won't be your local airport of course, (still going to say it: Spacecraft are not airplanes and airplanes are not spacecraft) but it's vastly more similar to say a military airfield than a launch center and that has operational and economic benifits that shouldn't be ignored. Secondly, while long unproductive coast phases should be avoided you're doing something here and as long as the advantages outweigh the disadvantages...

Having said that you'll point out that we then need to define and weigh those factors and I'll agree but they aren't as clear as one might think which is why actually testing this might be handy. I saw you mentioned that you'd like to 'see' this in operation before beliving it might work?

And I'll call you on using DCX as "proof" that vertical launch doesn't have to be more complicated than horizontal, you can even throw in Grasshopper/Starhopper in if you want. I can show you a video of the SR71 taking off from a standard runway, can you show me a Falcon 9 launching from an open field? From where the Grasshopper is launched from? How about Starhoppers pad? No? Might that be that because none of those VTVL 'proof-of-concepts' were really "proof" since they didn't have a fraction of the capabilty of an actual orbital launch vehicle?

The anwer is very much yes since those doing the experiments were pretty explicit (well outside the zelous advocates who are the ones touting this as proof while the acutal engineers shake thier heads and keep a low profile) that these were NOT aimed at proving effective launch but LANDINGs. (With some operational proofs along the way but still not orbital launch) I understand what you're trying to say, (as well as Archibald) but lets not fly off the handle by claiming the EZrocket (https://en.wikipedia.org/wiki/XCOR_EZ-Rocket) proves that the Space Shuttle could take off from my backyard :)

Lastly let me finish up on the more 'proper' rendzvous and transfer system. Martin I belive you said something like you'd like to see it before you belive it to paraphrase? Well in the case of rendzvous I'm sure you've seen dockings and missile intercept footage and while this would not be slow as the former it wouldn't be as violent and difficult at the latter either. Both vehicles are travelling in essentially a vacuum less than 100 yards apart on essentially the same vector and speed. They can be brought together within seconds with zero relative velocity at a distance of a few feet. And here's where you'd need an actual dedicated transfer system because the next part has to happen accuratly, fast and relatilvy simple.

Seen skydivers link up and hold hands? Same principle. Each vehicle would extend a "probe" ending in gripper which would lock together. In the 'palm' of these systems is the transfer coupling and tube which extends a few inches, vavles open and propellant flows. Since it is similar mechanically to the boom A2A system, (https://en.wikipedia.org/wiki/Aerial_refueling#Operation) you're looking at rates of 6,550lbs or more a minute. I don't of course have my original notes handy but I calculated that using a standard high speed option the entire transfer would take under 60 seconds. The equipment needed to do this is pretty straight forward and since you have 'cooperative' rather than competative systems accuracy and speed goes way up.

More later, thanks

Randy
 

martinbayer

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Randy,

I never questioned the potential feasibility of the concept, but instead of qualitative arguments and analogies I still want to see a *quantitative* mass and cost comparison of both concepts for the same technology level, design assumptions, and mission requirements to drive out advantages as well as disadvantages of different configurations and allow clear conclusions as to which architecture is ultimately preferable. Assuming for example identical vehicles for the tanker and orbiter, obviously the same orbiter design driven booster mass and complexity issues as for the TSTO occur. Conversely, the use of H2O2 and kerosene for a conventional TSTO would allow to fit a propellant module into the booster cargo bay as well. Likewise, there have also been rocket powered HTHL TSTO concepts with runway takeoff, see for example AIAA 2004-3731. With respect to exhaust plume interaction of parallel stages, I believe that the Falcon Heavy with 27 rocket engines firing in parallel from liftoff to altitude in three separate stages demonstrates that any related potential issues are manageable. That's why consistent assumptions are vital for a truly fair comparison.

Martin
 
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RanulfC

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Randy,

I never questioned the potential feasibility of the concept, but instead of qualitative arguments and analogies I still want to see a *quantitative* mass and cost comparison of both concepts for the same technology level, design assumptions, and mission requirements to drive out advantages as well as disadvantages of different configurations and allow clear conclusions as to which architecture is ultimately preferable. Assuming for example identical vehicles for the tanker and orbiter, obviously the same orbiter design driven booster mass and complexity issues as for the TSTO occur. Conversely, the use of H2O2 and kerosene for a conventional TSTO would allow to fit a propellant module into the booster cargo bay as well. Likewise, there have also been rocket powered HTHL TSTO concepts with runway takeoff, see for example AIAA 2004-3731. With respect to exhaust plume interaction of parallel stages, I believe that the Falcon Heavy with 27 rocket engines firing in parallel from liftoff to altitude in three separate stages demonstrates that any related potential issues are manageable. That's why consistent assumptions are vital for a truly fair comparison.

Martin
Thanks Martin as I noted it was a flyby so I only hit the high points for brevity. (If you've seen some of my other posts you'll know what I mean :) )

I'm still reading both the thread and the articles... God help me I'll need a bit to process the citations as well but I will persevere.. I hope :)

My personal suspicion in any comparison, (so take it for what it's worth... my opinion and forums posts seem to improve plant health and growth so there is THAT going for me :) ) is that the sub-orbital refueling is going to lose in several categories from the simple fact it's an odd concept and seems operationally complex. Having said that there's an operational and logistical reason it keeps cropping up in military circles along with "Blackhorse" like concepts. The actual 'best' choice is often customer rather than concept driven :)

Still I'll see if I can find my notes and such for input and discussion.

H2O2/kerosene CAN be used in either configuration as Clapp pointed out in his studies on configuring HTHL/VTHL and VTVL SSTO concepts, the fact he was aiming those concept at military operational utility were in fact the whole point. He concluded, (and for the majority of operational requirements the Air Force agreed in principle) that for pure rocket power VTHL or VTVL concepts were the best. Once any type of airbreathing propulsion was added HTHL was the top pick.

I googled the cited report (AIAA 2004-3731, "The Formation of a Near Term Stepping Stone to a Low Cost Earth-to-Orbit Transportation Based on Legacy Technology" correct?) and can't recall from the cover page if I've read it or not. I know I've seen similar ones though and I'll point out that while rocket powered HTHL systems are considered unless there's something ground breaking in that one they are always behind airbreathing HTHL concepts specifically due to the operational and physical issues with rocket powered horizontal take off. They do make a come back with any type of take off assistance system, (catapult, rail system, EM launcher etc, btw my favorite is actually a rather elegant one called CELT or Closed End Launch Tube that's actually air powered, it's surprisingly efficient) but otherwise are to operationally and economically limited compared to vertical rocket powered take off.

And that's a point here because while there's some restrictions to the general operations plan this is a concept that CAN take off from a regular airport and go into space. (No this does NOT make it an airplane nor give it "airplane like" economy/operations. Closer but still not going to be that golden bullet at least not at first)

And the point on rocket plume interaction is not that it can't be managed but that it HAS to be managed. No exception. Along with that you MUST take into account and manage the hydraulic and aerodynamic stress' of the joined AND separate bodies from launch to vacuum due to possible abort scenarios. You have to account for shifting CG, liquid slosh and other variable along the whole flight trajectory for two different vehicles. The list goes on and the point really is still going to be NOT having to do so makes things a lot more simple and less costly. You don't get that choice in a two stage vehicle, a "single stage" vehicle will always be less complex and operationally simple in that context. (Note I also don't advocate for SSTO concepts. T+STO vehicles will always have better margins bu that doesn't necessarily render ALL the SSTO advocates arguments invalid... Just most of them :) )

Consistent assumptions (and clarity between those discussing those assumptions I might add :) ) ARE vital to a fair and balanced assessment/comparison of concepts, and even in a friendly forum discussion I agree that one should attempt to provide numbers if one can to help that along. Quite often the problem is obtaining those number with sufficient consistency for the purposes especially when one has no actual (white tech world) prototype or example to work from. But I'm going to quote someone with a deeper and broader knowledge of the subject than I in regards to obtaining that 'fair' comparison:
There is a reason why some concepts are studied significantly more often and in far greater depth than others. "Fairness" has nothing to do with it, it is more based on which ones are deemed promising and which ones aren't.
As I've noted while this concept doesn't often come up in commercial or "civilian" circles it (and variants thereof) DO come up in military work for the reason you note :)

Do I think it's a slam-dunk solution to GTO flight? Not at all but I think it deserves a look and I'd like to try and wring it out for that purpose. :)

And now I must off to do the bidding of my masters and produce food... Oh and feed the wife too I suppose if the cats allow it. I'll check back and thanks for the discussion

Randy
 

Archibald

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thanks RanulfC for his explanations... he is far better at arguing / quoting / nailing a point - than myself (short temper doesn't help, welcome to my Greta Thunberg side).

that the sub-orbital refueling is going to lose in several categories from the simple fact it's an odd concept and seems operationally complex. Having said that there's an operational and logistical reason it keeps cropping up in military circles along with "Blackhorse" like concepts. The actual 'best' choice is often customer rather than concept driven
bingo. I fully agree with that point of view. What I'm suggesting in my papers is that rocketplane has plenty of niches it could fill.

the whole thing is an evolutive family of rocketplanes.
evolutive by oxidizer changes and also by adding birds into the flock : 2 to 3, 3 to 4 and eventually 8.
 
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Archibald

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Since it is similar mechanically to the boom A2A system, (https://en.wikipedia.org/wiki/Aerial_refueling#Operation) you're looking at rates of 6,550lbs or more a minute. I don't of course have my original notes handy but I calculated that using a standard high speed option the entire transfer would take under 60 seconds. The equipment needed to do this is pretty straight forward and since you have 'cooperative' rather than competative systems accuracy and speed goes way up.
aaaah that's fantastic. We need to discuss that further !!! unbelievable. I think we should marry that with boom rendezvous.
 
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Archibald

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I googled the cited report (AIAA 2004-3731, "The Formation of a Near Term Stepping Stone to a Low Cost Earth-to-Orbit Transportation Based on Legacy Technology" correct?) and can't recall from the cover page if I've read it or not. I know I've seen similar ones though and I'll point out that while rocket powered HTHL systems are considered unless there's something ground breaking in that one they are always behind airbreathing HTHL concepts specifically due to the operational and physical issues with rocket powered horizontal take off. They do make a come back with any type of take off assistance system, (catapult, rail system, EM launcher etc, btw my favorite is actually a rather elegant one called CELT or Closed End Launch Tube that's actually air powered, it's surprisingly efficient) but otherwise are to operationally and economically limited compared to vertical rocket powered take off.
and that's why I suggest to use plain old turbofans for an airliner-style liftoff - and nothing else. The RASV shows that exotic ground assist systems are unwelcome at air bases and airport. They need and want F-16 or 737 ground ops.

Incidentally, let me present myself.
Aged 37, Archibald not my real name. Graduated in archivistics, english and spanish languages (I'm french) and more recently, in logistics. Recently accomplished a lifelong dream of landing a job in aerospace. I am presently working as a logistic manager for a contractor of a low-cost airline (not Ryanair but a fast-growing competitor of them in Europe).
 
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Archibald

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In essence the concept is an 'assisted' SSTO using two near-SSTO's and propellant transfer instead of a dedicated booster and orbiter. (Everything is an orbiter) In the cited early Bi/Trimese studies the use of orbiters as boosters was a major efficiency issue (and this is still true today) because the 'booster' now had mass and complexity it didn't need even though in 'theory' it could be used as an orbiter as well. In truth, and especially as most studies used LH2, trying to pack the 'booster' propellant in the payload bay didn't work so you ended up with having to have a dedicated "booster" and orbiter airframe with all the design and development costs therein. As cost scales with airframe size in aerospace a set of smaller airframes is going to be less costly than a single large one. (Operationally it can be argued they'd come in at a lower overall cost as well)
Brilliant. I have to aknowledge, I WANTED to say it like this, but I FAILED. This is really what I had in my mind when saying bimese and trimese are "suboptimal" at the beginning of the thread. The reason why NASA rejected the Triamese by April 1969.
 

Archibald

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One of the other papers waxed lyrical on the possibilities of refuelling in low Earth orbit. Arthur C Clarke remarked back in 1947 that once you reach low Earth orbit you are halfway to anywhere [in the Universe]. It takes just half of the Earth's escape energy budget to reach LEO. Given a single top-up to reach LEO, you need two more to make it to interstellar space. Old news, but there you go.
This. My papers mentions that point. Going from Earth surface to Earth orbit takes an horrible delta-v of 9 km/s. By comparison, Earth escape is 3 km/s, lunar orbit is 4 km/s and lunar surface, 6.5 km/s.
Now follow my reasoning.
Since the rocketplane is build for suborbital REFUELING, then the refueling gear can be used a second time once in a stable Earth orbit. Orbital propellant depot, here we go. Filled with kerosene and H2O2, which don't boiloff with time, unlike cryogens.
Let's suppose we fill the tanks to the brim. See my calculations up thread: total delta-v of the Mk.1 with the tanks full is 6100 m/s. Now if you refill the tanks completely, you regain these 6100 m/s.
So the question is, how far can you go from LEO with a delta-v of 6100 m/s ? see above. You can nearly land on the Moon. You can certainly go in and out of lunar orbit (4km/s +1 km/s TEI), returning via a mix of propulsive braking (1km/s left) and aerobraking.

In the end the most exciting aspect of the system is that, with only two refuelings (first one, partial, in suborbital flight, second one, complete, in orbit) you can fly all the way from Earth surface to cislunar space.
And with a third refueling in cislunar space, you can make the roundtrip from lunar orbit to surface to orbit (2.5 km/s down, 2.5 km/s up). Landing on the Moon Starship style, like a vertical tail-sitter, on throttled down rocket power.

Three refuelings, same rocketplane all the way from Earth surface to Moon surface.

What's more, since the delta-v to Earth escape (3 km/s) and lunar orbit (4 km/s) are so much smaller than ascent to orbit (9 km/s) then the payload rise accordingly. The hardest segment is ascent to orbit, and that's where payload suffer the most. By contrast, payload from LEO to cislunar space can be huge. It is a matter of getting out of Earth deep gravity well, or at least to the edge of it. We are living at the bottom of a steep gravity well.
 
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martinbayer

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Hello Randy,

thanks for explicitly stating that you think suborbital refueling might only be of interest for a military niche application! I think that puts that concept squarely into a box that excludes civilian/commercial applications (which I expect and hope will dwarf any other space endeavours in the future), just like aerial refueling is used nowadays by the military only, but by exactly none of any and all commercial airlines anywhere around the globe. Your points about the oh so difficult resolution of various stages firing in parallel were successfully resolved for the Space Shuttle decades ago, so this is just an engineering issue we already well know how to address. You state that rocket powered HTHL systems are considered to be always behind airbreathing HTHL concepts specifically due to the operational and physical issues with rocket powered horizontal take off, so why do you advocate horizontal launch for an in flight refueling architecture? And if you assume airbreathers, would you be willing to accept them for one concept but not the other, and if so, why? Whether airbreathers are preferable for horizontal takeoff or not, that question clearly affects the the identical tanker concept twice as much as an optimized nonidentical TSTO, or at least the same as in a clone bimese stage version. My personal conclusion is that airbreathers excel at steady state flight at subsonic, supersonic, and perhaps even hypersonic flight, while rockets shine at pure acceleration, which is at the heart of any space launch mission. I can relate to the cat dominance issue though :) .

Martin
 
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Archibald

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I think that puts that concept squarely into a box that excludes civilian/commercial applications
I don't think so. If the military can loft 12 000 pounds of satellites into orbit this way (see the screenshot I posted up thread), there is no reason the civilian market can't loft 12 000 pounds of... passengers later on.
I agree, let's the military pioneer the risks and we shall see.

just like aerial refueling is used nowadays by the military only, but by exactly none of any and all commercial airlines anywhere around the globe.
I disagree with that point of view. NOT about what you say - correct, no airline uses aerial refueling - but the rejection of aerial refueling as risky for the passengers.
Space travel is inherently risky. If we want to ferry tourists in orbit, risk will be superior to airline flight. Riding a Starship will be far riskier than taking a ride in an A380.
Then, I can't see why the risk of refueling would be more *unacceptable* than any of the other risk of classic rocketry or human space travel. Note that Ranulf mentions how the system abort modes are extremely begnin, as underlined by Jon goff here

The nice thing about such a setup is that if you do things right, most worst-case failures result in an aborted mission, not a loss of vehicle.

If one of the TSTO pairs doesn’t ignite when air-dropped, you abort (with the upper stage from that TSTO combo having enough propellant to make it home, and you only have to figure out what to do about the first stage).

If you can’t mate up in time, you abort.

If the QD doesn’t work, you abort.

If you can’t keep the vehicles together exoatmospherically, at worst the boom/hose fails, and you use hydraulic fuses to keep that from becoming a loss of vehicle event.

Now, there are many more things that can cause an abort in this scenario, but many of them are things that should get more reliable with practice.
----------------------------

More on the military mission. What I have in mind for a twin keroxide Mk.1 rocketplane is very much something akin to
- Bantam (NASA)
- Rascal (USAF)
- Falcon (USAF)
- ALASA (Clapp was involved in this one, incidentally !)
- XS-1 (DARPA)
Or, reaching further in the past...
- TAV (Trans-Atmospheric Vehicle)
- ALSV (Air Launch Sortie Vehicle)
- ISINGLASS
- Aerospaceplane

Back in the 80's at Langley James A. Martin called it "orbit on demand". More recently it is called "responsive space".

What I mean is that the basic obsession of USAF with spaceplane is
- takeoff from any AFB
- go into orbit
- drop the satellite
- return to AFB
- refurbish, maintenance, 24 hours, rinse, repeat.

That's their absolute Holy Grail since 1959.

Well, then a turbofan+rocket spaceplane, with a suborbital refueling, is the one and only system that can achieve that dream, 100%. I mean, it checks every single box above.

Get the rocketplane out of the hangar with its payload. Fill it with kerosene, then with H2O2. Light the turbofans, climb to 50 000 ft, mach 0.95, raise the nose to 30 degree above the horizon, light the rocket, shut the jets, climb to 5 km/s and 50 miles.
There, throttle down, perform a brief oxidizer transfer via an identical "buddy" tanker.
Throttle-up again, ascent to orbit, drop the satellite.
Then re-enter the atmosphere, land on turbofan power at any airstrip under the trajectory. Once on the ground, take a load of kerosene, and fly subsonically back to the launch site.
Alternatively, you could load a C-5 or a C-17 with a large tank of H2O2 and send it at the landing site. There it meets with the rocketplane and pass it a load of oxidizer. This would allow for a new mission to proceed !

The CONOPS is simple. The only tricky part is the refueling. That's simplicity, is why I like this concept so much.

Suborbital refueling is not even necessary if you replace it (and the buddy tanker) with an expendable upper stage.
The twin flaws however, in this case are
a) the rocketplane don't go into orbit
b) the upper stage is expendable
Still an interesting solution to launch loads of cubesats. That's the exact shift Clapp and Zubrin made in 1996 when going from "Black Horse - speculative idea" to "Black Colt / Pathfinder." Unfortunately they were wrong.
"Suborbital refueling via a buddy tanker" is far more interesting than "subsonic refueling + expendable upper stage".
Yet Clapp and Zubrin picked the second solution in order to not scare commercial customers - after the Air Force abandonned the Black Horse concept.
 
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martinbayer

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Archibald, or whatever your real name is,

*please* don't put words in my mouth/writing - I never claimed that aerial refueling was risky for airline passengers, but simply observed it wasn't done *at all*. Likewise, I expect future aerospace passenger operations to be done with a minimum amount of vehicle interactions, because the more, the messier.

Martin
 

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It wasn't intentional. I haven't Ranulf talent for quoting and arguing. And making mile long, multiquote posts. :p

Should have said this
but the rejection of aerial refueling -- for passengers transportation
I wanted to say it could happen if necessary, provided the military clear any risk beforehand.
 
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steelpillow

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Arthur C Clarke remarked back in 1947 that once you reach low Earth orbit you are halfway to anywhere [in the Universe].
AhhhHEM there mister, want to correct that before Bob comes down from heaven and set you straight? :)
Well, OK it was 1950 and maybe the phrase "halfway to anywhere" might have come later, but I refer you to his Interplanetary Flight, Temple Press, 1950, page 15:
"The necessary speed to maintain a stable orbit at any distance from the Earth ... is about 7.9 km/sec (18,000 m.p.h.) This is less than the corresponding escape velocity in a ratio 1:√2."
Since e=½mv^2, the kinetic energy to reach LEO is half that to reach escape velocity. In practice some extra energy is needed to climb to orbit so the kinetic energy equation is an approximation to the practical launch, but the difference is relatively small. Even if the craft is refuelled in LEO (as Archibald sensibly suggests), that fuel has already been given a lot of expensive kinetic energy to get up there. The velocity delta from LEO to escape may be less, but the total energy cost still has to be found. I accept that in this scenario, the "second" fuel load which I observed is needed for escape has already been burned by the tanker.

Many thanks to you and Archibald for your own contributions here, very informative. However I still find unsupported claims lurking. Every engineer knows that in a chain of 100 links, if one link fails the whole chain fails.
  • "Operationally if the notional TSTO fires all engines on launch and has propellant cross-feed to seperation then the analogy works but that has its own issues to deal with. (Exhaust plume interaction and aerodynamic and hydraluic stress' for example)" is an excellent description of the Space Shuttle. It cannot be seen as damning criticism.
  • "Your abort options are greater since you don't have to worry about seperating a mated pair of vehicles should something go wrong." Setting aside the SRB (which ran counter to Von Braun's dictum never to use solid fuel), I cannot recall a step-rocket launch where escape separation ever failed. And if something goes wrong with the sub-orbital refueling, you do have to separate.
  • "I saw you mentioned that you'd like to 'see' this in operation before believing it might work?" No, I said I'd like to see the numbers.
  • An open runway vs a dedicated launch facilities, eh? The runway may be simpler to engineer but the craft itself is a heck of a lot more complex with its wings, airbreathing engines, retractable undercarriage and other flight systems. Again, directly comparable quantitative analyses of the whole system lifecycle (air traffic control, safe fuel storage, so many peripheral activities are involved) are needed before one can accept the best answer. I am not prepared to commit based on speculative arguments alone.
  • Composite vs refuelling? Refuelling a jet fighter in mid-Atlantic is done because the jet is not equipped for composite carriage. By contrast the Short Mayo of the interwar period was a transatlantic composite flying boat, Mercury a modified Empire class flying boat, Maia a dedicated mail-carrying floatplane. It was done that way because in-flight refuelling was deemed overly expensive. Not even commercial freight uses in-flight refuelling today, it is nothing to do with passenger safety, it is just too expensive. Using the qualitative example of the jet fighter optimised for combat to try and justify the economics of in-flight refuelling is absurd.
None of these niggles is a technical engineering showstopper, but I do seriously doubt the economics of it.

On the plus side, I would note the incredible speed with which a Formula One racing car gets refuelled during a pit stop, something like 3.9 seconds including attachment, transfer and detachment. Fortunately perhaps, a spaceplane does not need all four tyres changing at the same time. ;)
 

Archibald

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Well, OK it was 1950 and maybe the phrase "halfway to anywhere" might have come later, but I refer you to his Interplanetary Flight, Temple Press, 1950, page 15:
"The necessary speed to maintain a stable orbit at any distance from the Earth ... is about 7.9 km/sec (18,000 m.p.h.) This is less than the corresponding escape velocity in a ratio 1:√2."
Since e=½mv^2, the kinetic energy to reach LEO is half that to reach escape velocity. In practice some extra energy is needed to climb to orbit so the kinetic energy equation is an approximation to the practical launch, but the difference is relatively small. Even if the craft is refuelled in LEO (as Archibald sensibly suggests), that fuel has already been given a lot of expensive kinetic energy to get up there. The velocity delta from LEO to escape may be less, but the total energy cost still has to be found. I accept that in this scenario, the "second" fuel load which I observed is needed for escape has already been burned by the tanker.
The trick is to haul the propellant depot.. propellant through varied means.

For example, if you add more refueling to the dance - 3, 4 or even 8 rocketplanes - then the massive FLOC effect happens - on payload. And the final rocketplane reach orbit with a large amount of prop left in the tanks. In a nutshell, that orbiter become... a tanker, which internal fuel can be pumped into a depot or another rocketplane headed for the Moon.

Another solution is to use a dumb expendable rocket stage shot from the back of the rocketplane in suborbital flight. Once the stage reach orbit, it becomes... a depot. Then dock many of them around a central truss, and there you are, a prop depot.
 
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steelpillow

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then the massive FLOC effect happens
Hyperbole like that does not help your case. The efficiency/payload gains from flock refuelling are exactly the same as the gains from stage refuelling.
Consider this thought experiment: Tie all flock members together with very long pieces of wire. As you use them up, drop that wire so they can go back home. Now shorten the wires a bit for the next launch. Same efficiency. Shorten the wires a bit more. Same efficiency. Eventually, shorten the wires to barely anything, less than a mm. Same efficiency. Now shorten the wires to zero, i.e. clamp the whole flock together. Are you seriously suggesting that the act of clamping massively changes the efficiency? Or that efficiency is a function of wire length?
Consider it another way. A 2^n flock requires 2^n tankfuls of fuel. or (2^n)-1 if the orbiter takes off near-empty. Put say 55% (4) of those tankfuls in the first stage, 30% (2) in the second and 15% (1) in the orbiter. That uses the same discard cycle and packs the same energy punch as an n=3 flock with the orbiter launched near-empty. The total energy cost of getting all your hardware that far and that fast still has to be found, with or without joining wires.
Sure both these options are miles better than an SSTO that lugs all the hardware all the way, but that is not the point. There are enough doubts over the value of SSTO operation as it is.

Your "depot" is exactly how space stations get constructed today. For example much of the ISS facility began its life as Ariane second stages. SpaceX are planning to do something similar to your refuelling depot with the Mars expedition. But that is not suborbital and is off-topic here.
 

Archibald

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I would like to post some of the spreadsheets but for reasons beyond my understanding, this forum don't want to attach either Excel or Open Office calcs. Not recognized. :mad:
 

Jemiba

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I just tried to attach an Excel file and it worked ... though it's nor mentioned in the "supported file types".
 
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