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Suborbital refuelling

Archibald

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You guys are great, really.

this morning I made an interesting exercise. Related to "carrier aircraft / airbreathing engine speed" vs "delta-v gain"
because, you see, the two are not proportional nor linear.

Let's take the case of Skylon. The airbreathing engines push rocket ignition to Mach 5.5. ok, then how much delta-v to orbit GAIN is mach 5.5 ?
Mach 5.5 is 1.87 km/s.
Now follow my reasonning: Clapp says going to Mach 5.5, airbreathing, lowered the delta-v to orbit to 20700 ft/s. Which is 6.3 km/s. From 9.3 km/s, that's a delta-v gain of 3 km/s. Problem: Skylon was supposed to gain only 1.87 km/s, not 3 km/s !

so the cool news is that the delta-v gain from carrier / airbreathing, grows faster than the carrier / airbreathing own speed.

In clear english: launch from a Mach 0.95 carrier provides a delta-v boost of much more than Mach 0.95. Well, here comes (again) Marti Sarigul Klinj
Mach 0.95 carrier brings +1100 m/s bonus on the way to Earth orbit (8.1 km/s left - from a ticket of 9.2 km/s, average)
Mach 2 carrier brings+1600 m/s bonus (so 7.6 km/s left)
Mach 3 carrier brings + 2000 m/s bonus (so 7.2 km/s left)

And we could add Burnside Clapp and Skylon coinciding results

Mach 5.5 = 1.87 km/s brings +3 km/s bonus (so 6.2 km/s left)

What is sure is
- Subsonic, supersonic, and low hypersonic represents three very different flight regimes, harder and harder.
- Meanwhile the rocket equation has a logarithm so it is non linear, too, just like the different mach regimes.

The basic rule is: the deeper into hypersonic, the harder, while the rocket equation non-linear nature just watch you heating the heat barrier, smiling.
High speed flight is as unforgiving as is the rocket equation.
airbreathing boost vs delta-v gain.PNG
 
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steelpillow

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Isn't the ISS replenished with LOX?
ISS needs oxygen only for the crew. It has various onboard systems for that, with storage being either chemical (e.g. as water) or gaseous. Replenishment is usually by sending up more water, although I suppose it is possible that gas canisters were once sent up when a lot was needed in a hurry after some mishap or other. Neither liquid nor high-speed transfer nor even fuel.
 

steelpillow

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Mach 0.95 carrier brings +1100 m/s bonus on the way to Earth orbit (8.1 km/s left - from a ticket of 9.2 km/s, average)
A heavily-laden subsonic carrier would start to create shockwaves around Mach 0.8, with say 0.85 the max to avoid significant interference with the separation dynamics. Moreover it would be lucky to reach 50,000 ft (15,000 m) where the speed of sound is 330 m/s (depending on local temperature), so separation would take place at around 280 m/s. (540 kn) Not sure how that impacts your numbers.
 

Archibald

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Good point. It is important to make the distinction between, as you say " A heavily-laden subsonic carrier " and a rocketplane with integrated jet propulsion (think Astroliner or Pathfinder or Black Colt). The second one would not give a rat about the issue you mention, obviously.
Of course it pays a weight penalty to that, since air-launch leaves the heavy jets and most of the undercarriage weight to the mothership instead of carrying that burden into orbit.
 
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Archibald

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ISS is refueled in *storable propellants* by Progress ships. A legacy of Mir and Salyut reaching back to 1978 and Salyut 6. First orbital prop transfer between spaceships.
Bar storables, and for all the intensive talk about prop depots from Apollo EOR to ULA and Jon Goff, nothing else has been achieved so far.
Elon Musk is presently the most serious contender to unlock the prop depot, and he will do it grand scale: in order to go anywhere beyond LEO, Starship will need a transfer of 1100 mt of methalox, both mild-cryogen around -180°C.
 

steelpillow

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ISS is refueled in *storable propellants* by Progress ships. A legacy of Mir and Salyut reaching back to 1978 and Salyut 6. First orbital prop transfer between spaceships.
LOX is not a "storable propellant" in that sense. Also, the propellant they replenish is only for the manoeuvring thrusters, it is not spaceship propellant within the meaning of the phrase. And one does wonder whether any of its predecessors might have had their thrusters topped up.
 

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I never said LOX was storable propellants. Nuance: I said the only in-space refueling done, past and present, had been with storable props.
 

Archibald

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Back to suborbital refueling. After that major blunder in the spreadsheet, a major shift has happened.

The Mk.1 keroxide bird can't go to orbit unless 3-FLOC (and even 4-FLOC with a valuable payload). Not practical.
So I have decided to *downrate* those birds to
- suborbital tourism, Blue Origin or SS2 on steroids (5 km/s rather than 1 km/s)
- suborbital P2P passenger transportation with ricochet trajectories
- satellite launch using expendable upper stage
- flight testing of Mk.2 technologies plus future pilots training
Still for these missions they remain civilian airports darlings, using kerosene, H2O2, and civilian turbofans like the BR715, LEAP, or JT8D. Those engines give a 1100 m/s boost, lowering delta-v to earth orbit from 9200 m/s to 8100 m/s. Still not enough to fill the "spreadsheet blunder" and going into orbit.

Now the case of the Mk.2 kerolox bird.
The blunder also affected it, in the 2-FLOC configuration it still can't make it to orbit. So I have decided to turn it into the military prefered bird. Which mean: LOX, but also, to compensate, trade the quiet, civilian turbofans for
- noisy, afterburning F-110s which give Mach 2 capability before rocket ignition. In turn, this lower the delta-v by 1600 m/s, from 9200 to 7600 m/s.
- J58 push that to Mach 3 and beyond, a gain of 2000 m/s+ to 7200 m/s.
- MIPCC and/ or SERJ push to Mach 4+ and get the delta-v to orbit even lower, -360 m/s which bring it to 6900 m/s

Finally is the Mk.3 hydrolox bird. Since it can use a SABRE, it can lower the delta-v to orbit to 6300 m/s.
But there is no asolute need to go so far, because its superior specific impulse saved it from the *blunder* - it still easily get into orbit as 2-FLOC with a decent payload. Lucky me !
So the Mk.3 also work with all the Mk.2 alternate engines - from civilian turbofans to MIPCC and SERJ.

In a nutshell, I shamelessly use the "air launch / airbreathing boost" to compensate for my "spreadsheet blunder". This is tolerable and not dishonest ONLY because I used proven data by respectable people (Clapp, MSK, also Sorensen / Bonometti air-launch study, DARPA and others).

Note that some criss-crossing between the three variants are possible: for example SERJ used peroxide, just like the Mk.1. But SERJ, like SABRE, must be insanely noisy. the military care less, but civilian airports... forget it.

Basically the Mk.1 keroxide bird has taken such a huge hit from the "spreadsheet blunder" I'm not sure even a Mach 2 or Mach 3 "airbreathing boost" (read, F110 or J58) could send it in orbit AGAIN, in a 2-FLOC configuration.
It would probably take a MIPCC or SERJ at Mach 4 to do it again.
But these engines open a new can of worm: Mach 4 in the atmosphere means the structure hit the heat barrier, even briefly - before lighting the rocket and getting out of the atmosphere; we are not discussing a LAPCAT long range cruise here.

So the philosophy is "forget going into orbit with the Mk.1, keep the civilian turbofans for airports even if all missions will be non-orbital". C'est la vie.
 
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steelpillow

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I never said LOX was storable propellants. Nuance: I said the only in-space refueling done, past and present, had been with storable props.
Bear in mind that you had just said that "Isn't the ISS replenished with LOX? I thought I'd read that somewhere but could be wrong that LOX was brought up on the Progress along with the RCS propellant." and the only current use for LOX in space is as a propulsion oxidiser. You may not have said "2+2=5" but taken together that was what your posts implied. Other readers may not be aware you didn't mean it that way.
 

Archibald

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RanulfC would it be possible to run MIPCC on H202 rather than LOX & water ? At least SERJ has H2O2 right from the beginning (1967 !) which really help my case.
I personally like both of them very much. The neat thing with MIPCC, if you graft that on a stock F110, then you can turn a Mach 2, 1600 m/s delta-v boost into a Mach 4.5 one (around 2400 m/s) using the same basic engine. See my last post: in the case of the doomed Mk.1 bird, MIPCC would save the day and allow it back into orbit in the 2-FLOC scheme lost to my silly spreadsheet blunder.
 
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Archibald

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Yes, this one. Welcome aboard this ship, Michel Van.

I've redone the (doomed) Mk.1 keroxide vehicle with all the different engines. Basically, if the airbreathing boost doesn't carry it to Mach 3 (2000 m/s > 7200 m/s to orbit) then it can't make it. Zero boost (9200), subsonic boost (8100) and Mach 2 boost (7600) = it's dead, Jim.
Then Mach 3 barely makes it, leaving really MIPCC (Mach 4) and SERJ (Mach 4.5) as saviors. Can't use Mach 5.5 SABRE here, because LH2 & LOX.
 

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Archibald

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Variants of the ROLS – Reusable Orbital Launch System

ROLS Mk.1

Keroxide props for all of them. With BR715 or JT8D civilian turbofans it is very "airport friendly" but can't go into orbit even as 2-FLOC. Used instead as pilot trainer, tech demonstrator, space tourism, P2P passenger transport with ricochet trajectories, and satellite launch with expendable upper stage.

Mk.1A
In order to restore orbital capability, F110 turbofans from the F-15E push rocket ignition to Mach 2.5. Still marginal to get any payload into orbit, but way to go for both SERJ and MIPCC variants (see below)

Mk.1B
The same F110s modified with MIPCC push rocket ignition to Mach 4 and greatly improve payload to orbit. Problem: MIPCC eats LOX and water for lunch, not peroxide. Two solutions: solution 1, drop tanks (one LOX, one water, X-15 style). Second solution: put the tanks into the payload bay, and they eat into the payload to orbit.

Mk.1C
Alternative to Mk.1B with SERJ. Little gain to Mach 4.5 and, most importantly, runs on peroxide, just like the rocket engine. So no drop tanks nor payload bay tanks.

ROLS Mk.2
No need for the civilian turbofans, they don't like LOX plus can't go into orbit just like the Mk.1. So go for the military only. LOX allows specific impulse of 359 seconds instead of 327, greatly helping payload to orbit. Basic Mk.2 has F110, too, same reasons as Mk.1A, way to go toward MIPCC and possibly SERJ.

Mk.2A
The MIPCC bird, with an advantage over its Mk1B counterpart: MIPCC and the rocket both need LOX ! Still a need for a water tank, same places: payload bay or drop tank.

Mk.2B
The SERJ bird, with a mirror issue: H2O2 and LOX are dissimilar. Maybe a LOX SERJ is possible, Marquardt had a hydrolox one for NASA before switching to the keroxide one for the military.

ROLS Mk.3
Two variants here.
The basic Mk.3 has hydrogen-burning modified F-110 turbofans and, thanks to the extremely high specific impulse of 460 vs 320 – 360 for the others, don't need the advanced MIPCC or SERJ to make it to orbit as 2-FLOC.
And then there is the Mk.3A which takes profit of the... Skylon SABRE. This allows it to push rocket ignition to Mach 5.5, and gain a boost of 3 km/s on the way to orbit, lowering the delta-v from 9.3 km/s to 6.3 km/s. Combined with the other huge gain provided by suborbital refueling, its performance even as 2-FLOC is quite impressive. And it works in synergy with its Skylon great brother, eventually introducing Skylon to the art of suborbital refueling...
 

Archibald

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Seems that H2O2 can find its way into a MIPCC system. Water in the compressor, and peroxide in the afterburner. Pretty cool. Preston "Hypersoar" Carter once again, RASCAL, MIPCC. Those studies are godsends, really.

Since MIPCC works equally well with LOX and H2O2 it suits both Mk.1 and Mk.2 birds. Yet in both case they need a water tank in the payload bay or, alternatively, a water drop tank. I can really live with that to get the Mach 4 boost out of plain old military turbofans in large scale service - to you, F110.

MIPCC peroxide.png
 

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RanulfC

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Isn't the ISS replenished with LOX?
ISS needs oxygen only for the crew. It has various onboard systems for that, with storage being either chemical (e.g. as water) or gaseous. Replenishment is usually by sending up more water, although I suppose it is possible that gas canisters were once sent up when a lot was needed in a hurry after some mishap or other. Neither liquid nor high-speed transfer nor even fuel.
Ok, good to know

I never said LOX was storable propellants. Nuance: I said the only in-space refueling done, past and present, had been with storable props.
Bear in mind that you had just said that "Isn't the ISS replenished with LOX? I thought I'd read that somewhere but could be wrong that LOX was brought up on the Progress along with the RCS propellant." and the only current use for LOX in space is as a propulsion oxidiser. You may not have said "2+2=5" but taken together that was what your posts implied. Other readers may not be aware you didn't mean it that way.
That was me :)

RanulfC would it be possible to run MIPCC on H202 rather than LOX & water ? At least SERJ has H2O2 right from the beginning (1967 !) which really help my case.
I personally like both of them very much. The neat thing with MIPCC, if you graft that on a stock F110, then you can turn a Mach 2, 1600 m/s delta-v boost into a Mach 4.5 one (around 2400 m/s) using the same basic engine. See my last post: in the case of the doomed Mk.1 bird, MIPCC would save the day and allow it back into orbit in the 2-FLOC scheme lost to my silly spreadsheet blunder.
As Michel Van noted it's been suggested but keep in mind the LOX injection wasn't for cooling purposes but to stabalize the flame-front in the afterburner (and combustors at high-altitude) which is a boost you wouldn't get from peroxide unless it's decomposed. Using a keroxide SERJ would mean a bit bigger peroxide tank if you're using it for inlet and AB injection though on the other hand you should have to worry less about the compressor face heating issues since the compressor isn't designed the same as a standard turbojet. Above about Mach 1.5 the SERJ is supposed to transition to pretty much pure ramjet mode till around Mach 4/4.5-ish depending on the design. The MIPCC system would boost your initial fan/ram/rocket thrust, while adjusting 'oxidizer' levels in the rocket motor(s) would adjust the levels for the AB/ramjet section of the engine.

Usage in a 'standard' turbojet gets you both increased thrust and a wider mach range for the compressor face/afterburner system which is what the whole "Steamjet" concept came down to.

Randy
 

Archibald

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Thank you.

I'm desperately looking for some tech papers about running turbofans on hydrogen... preferably recent ones.
 

Archibald

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Just for you to know, Jeff Foust from The Space Review answered me, nice fellow, encouraging, but I have to rework the thing into something shorter. I'm a little too maniacal on details.
 
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