The Coming SSTO's.

[Orionblamblam]

An SSTO with no payload mass is useless.

Well, maybe. If the SSTO is dirt-cheap, it might be a good way to delivery scrap aluminum and titanium to orbit for larger construction projects. It might make a good ASAT system if it can be guided adequately precisely.

Of course, an SSTO with no payload mass is on the razors edge of performance. Any weight gain or performance drop, and it's Single Stage to the Indian Ocean.

 

[Michel Van]

Michel - try browsing information on google about "kerosene as fuel for a SSTO", and you'll change your mind. You will REALLY want to be hard with RG Clark after that. Thrust me.

I know that some consider kerosene IS the fuel for rocket SSTO
why ? because it low volume it use, most SSTO proposals use Hydrogen as fuel because it higher power (on Skylon later)
Hydrogen need bigger fuel tanks, what led to higher aerodynamic drag during launch and lost on Payload
But sadly Kerosine has lower power as Hydrogen, what annihilates the profit
see also my note on this Kerosine SSTO proposal http://www.secretprojects.co.uk/forum/index.php/topic,13211.msg131521.html#msg131521

Some people made there thoughts about that and came up with some weird ideas:

tripropellant rocket: it's burns first Kerosine/oxygen then later hydrogen/oxygen with same engine, what reduce the rocket size and mass about 30%
impossible ?
nope the soviets built, the RD-701 with 5 Turbo pumps ! powered by 2 preburner (oxygen/kerosene)
Kerosine and Hydrogen have apart feed-line into the Burncamber, already from at ignition Hydrogen is used to cool the Burncamber.
you already notice the complexity of the RD-701 engine, what will have high cost on maintenance...

another idea was to launch a mini Shuttle with Kerosine/oxygen (or Kerosine/ hydrogen peroxide) tanks partial fueled.
rendezvous subsonic with KC-135 tanker, who fill up the Tanks and the mini shuttle bast into orbit.
but that not a SSTO in the true sense

The use of Air for engines, here were allot proposals:
Like ramjets who burn Kerosine and air to mach 5, while rocket engine runs on reduce power.
A other idea was to scope in air, liquified it and pump into rocket engine to increase the thrust
the drawback you lose on Specific impulse, but you reduce the gravity losses on way up

and now to SKYLON http://www.secretprojects.co.uk/forum/index.php/topic,2455.0.html
there SABRE Engine are hellish breed between a conventional jet engine with a rocket engine.
It's breath Air and burn it with hydrogen, until speed of mach 5.5 then is use internal oxygen tanks to get mach 25. what reduce the space plane size and mass about 30%.
SABRE use a crossover of Ramjet and liquified mode on the edge of thermodynamics
it's need a internal Helium cooling loop to cope with heat losses.
you already notice the complexity of the SABRE engine, what will have high cost on R&D and maintenance...

 

[RGClark]

'''
Michel - try browsing information on google about "kerosene as fuel for a SSTO", and you'll change your mind. You will REALLY want to be hard with RG Clark after that. Thrust me.

http://www.google.fr/#q=%22The+Coming+SSTO%22&hl=fr&prmd=imvns&ei=3P8IULLhHOGK0AXy-dDCCg&start=10&sa=N&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=91c96fcb7ddaab89&biw=1024&bih=621

http://www.google.fr/#hl=fr&sclient=psy-ab&q=%22kerosene+fuel%22%22SSTO%22&oq=%22kerosene+fuel%22%22SSTO%22&gs_l=hp.3...5219.11026.0.11211.21.21.0.0.0.0.143.1301.19j2.21.0...0.0...1c.ew4psCEjCuU&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=91c96fcb7ddaab89&biw=1024&bih=621

http://www.google.fr/#q=%22kerosene+fueled%22%22SSTO%22&hl=fr&prmd=imvns&ei=OgAJUIS0OKnF0QXSg8zJCg&start=20&sa=N&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=91c96fcb7ddaab89&biw=1024&bih=621
...

Some of those links argue in favor of hydrogen for a SSTO, some in favor of dense propellants. SSTO's can be done now using either fuel.


Bob Clark

 

[RGClark]

This is well below the highest efficiency kerosene engines (Russian) we have now whose Isp's are in the 330's.

http://www.astronautix.com/engines/nk31.htm

Specific impulse: 353 s.

but this is only an upper-stage rocket engine. Maybe it is possible to combine this engine with an ED-nozzle so it could be used from launch to orbit.

I was referring to engines used for ground-launch such as the NK-33 and the RD-180. But as you say some altitude compensation methods may work to allow the even higher Isp upper stage engines to be used for ground launch.


Bob Clark

 

[aam641]

Then this version of the Falcon 9 first stage could lift 1,200 kg to orbit:


Then the Falcon 9 first stage could serve as a proof of principle SSTO on the switch to the Merlin 1D engine.

I think that this post can serve as the perfect example of why staged rockets are more cost-efficient and preferred by the industry.


Falcon 9 can lift about 10 tons into LEO and you need to sacrifice 10 engines and respective fuel tanks to do it. There is also the possibility of reusing 9 of them.


On the other hand, as your calculations show, Falcon SSTO would sacrifice about 9x8=72 engines and respective fuel tanks to achieve the same effect. And none of that can be reasonably reused.

 

[RGClark]

I think that this post can serve as the perfect example of why staged rockets are more cost-efficient and preferred by the industry.
Falcon 9 can lift about 10 tons into LEO and you need to sacrifice 10 engines and respective fuel tanks to do it. There is also the possibility of reusing 9 of them.
On the other hand, as your calculations show, Falcon SSTO would sacrifice about 9x8=72 engines and respective fuel tanks to achieve the same effect. And none of that can be reasonably reused.

Actually, you would not need all 9 Merlin 1D's to just lift the first stage. Using the 147,000 lb sea level thrust of the Merlin 1D, five of them would suffice. So you could subtract 4*450 kg = 1,800 kg off the dry mass. This would bring the dry mass now down to 10 mT and the mass ratio to over 25 to 1(!)
This probably would now be enough to add on reentry and landing systems to make it reusable and still carry payload.


Bob Clark

 

[RGClark]

...
The first stage propellant load is given as 553,000 lbs, 250,000 kg, and the dry weight as 30,000 lbs, 13,600 kg. The Merlin 1C mass hasn't been released, but I'll estimate it as 650 kg, from its reported thrust and thrust/weight ratio. The Merlin 1D mass has been estimated to be 450 kg. Then on replacing the 1C with the 1D we save 9*200 = 1,800kg from the dry weight to bring it to 11,800 kg.
The required delta v to orbit is frequently estimated as 30,000 feet per second for kerosene-fueled vehicles, 9,144 m/s. When calculating the delta v your rocket can achieve, you can just use your engines vacuum Isp since the loss of Isp at sea level is taken into account in the 30,000 fps number. Then this version of the Falcon 9 first stage could lift 1,200 kg to orbit:

310*9.81ln(1 + 250/(11.8 + 1.2)) = 9,145 m/s.

Then the Falcon 9 first stage could serve as a proof of principle SSTO on the switch to the Merlin 1D engine.

Bob Clark

We can probably do better than that first estimate of the Falcon 9 first stage with Merlin 1D's as a SSTO. The Merlin 1D has a 147,000 lb sea level thrust:

Modified Merlin engine completes full duration firing.
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: June 25, 2012
http://www.spaceflightnow.com/news/n1206/25merlin1d/

The gross mass of the Falcon 9 first stage with the Merlin 1D's and a 1.2 mT payload would be 250 + 11.8 + 1.2 = 263 mT, 578,600 lbs. This could be lofted by just 4 of the Merlin 1D's. But the thrust would be just a little over the gross mass resulting in high gravity loss. So let's use 5 Merlins. Subtracting off 4 Merlins makes the dry mass 11,800 - 4*450 = 10,000 kg.
The number of 30,000 fps delta-v for LEO is assuming a T/W ratio common for liquid fueled rockets, in the range 1.1 to 1.2. With all 9 Merlins the T/W ratio would above 2.2. This would result in a much reduced gravity loss. So the required delta-v would be less than the 30,000 fps number, and so actually higher than 1.2 mT could be sent to LEO even in that case.
But let's look at the case of using 5 Merlins. SpaceX has given a vacuum Isp of the Merlin 1D as actually 311 s. Then we could send 3.1 mT to LEO:

311*9.81ln(1 + 250/(10 + 3.1)) = 9,152 m/s.

SpaceX has said though they want to move to a larger version of the Falcon 9 called the Falcon 9 v1.1, in accordance with the Merlin 1D's larger thrust. The Falcon Heavy will use this version's first stage for its core stage and side boosters. SpaceX expects the Falcon 9 v1.1 to be ready by the end of the year.
Elon Musk has said the version 1.1 will be about 50% longer:

Q&A with SpaceX founder and chief designer Elon Musk.
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: May 18, 2012
http://www.spaceflightnow.com/falcon9/003/120518musk/

I'll assume this is coming from 50% larger tanks. This puts the propellant load now at 375,000 kg. Interestingly SpaceX says the side boosters on the Falcon Heavy will have a 30 to 1 mass ratio. This improvement is probably coming from the fact it is using the lighter Merlin 1D engines, and because scaling up a rocket actually improves your mass ratio, and also not having to support the weight of an upper stage and heavy payload means it can be made lighter.
So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass ratio is 30 to 1, which makes the dry mass 13 mT. Then this version can lift 6.7 mT to LEO:

311*9.81ln(1 + 375/(13 + 6.7))


Bob Clark

 

[Byeman]

What does this have to do with "Secret Projects"?

 

[Byeman]

Again you are making assumptions not based on reality. The strapon boosters will be the same construction as the core. They will not be optimized

 

[dannydale]

What does this have to do with "Secret Projects"?

I'm starting to wonder that too. ???

 

[Orionblamblam]

What does this have to do with "Secret Projects"?

That's a secret.

 

[Archibald]

Don't worry alls. Soon your worries will be drawned under a new barrage of nonsensical technical ramblings, complete with a whole bunch of internet links. And it will last for dozen and dozen of pages.
We are really living interesting times :

 

[RGClark]

Again you are making assumptions not based on reality. The strapon boosters will be the same construction as the core. They will not be optimized.

That seems reasonable to save on costs. But if that were the case why wouldn't they just say the lower stages, and so also the Falcon 9 v1.1 first stage, will have a 30 to 1 mass ratio?
Note that the mass the core stage will have to support for the Falcon Heavy is non-trivial. You have the 53 metric ton payload, but also the upper stage. Based on Falcon 9 upper stage gross mass of ca. 50 mT and the F9 v1.1 50% larger size, the upper stage in this case might be 75 mT. With the large fairing weight and interstage weight this would be over 130 mT.

Bob Clark

 

[RGClark]

What does this have to do with "Secret Projects"?

To the moderator, you may freely move the thread to the "Theoretical and Speculative Projects" forum if you wish.

Bob Clark

 

[RGClark]

...
So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass ratio is 30 to 1, which makes the dry mass 13 mT. Then this version can lift 6.7 mT to LEO:

311*9.81ln(1 + 375/(13 + 6.7))


Bob Clark

I didn't include the answer to that last calculation:

311*9.81ln(1 + 375/(13 + 6.7)) = 9,145 m/s.

Dr. John Schilling has produced a payload estimation program:

Launch Vehicle Performance Calculator.
http://www.silverbirdastronautics.com/LVperform.html

It gives a range of likely values of the payload. I've found the midpoint of the range it specifies is a reasonably accurate estimate to the actual payload for known rockets.
Input the vacuum values for the thrust in kilonewtons and Isp in seconds. The program takes into account the sea level loss. SpaceX gives the Merlin 1D vacuum thrust as 161,000 lbs and vacuum Isp as 311 s:

FALCON 9 OVERVIEW.
http://www.spacex.com/falcon9.php

For the 9 Merlins this is a thrust of 9*161,000*4.46 = 6,460 kN. Use the default altitude of 185 km and the Cape Canaveral launch site, and a 28.5 degree orbital inclination, to match the Cape's latitude.
Input the dry mass of 13,000 kg and propellant mass of 375,000 kg. Then it gives an estimated 7,564 kg payload mass:

Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Cape Canaveral / KSC
Destination Orbit: 185 x 185 km, 28 deg
Estimated Payload: 7564 kg
95% Confidence Interval: 3766 - 12191 kg

This may be enough to launch the Dragon capsule, depending on the mass of the Launch Abort System(LAS).

Bob Clark

 

[Byeman]

...
So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass ratio is 30 to 1, which makes the dry mass 13 mT. Then this version can lift 6.7 mT to LEO:

311*9.81ln(1 + 375/(13 + 6.7))


Bob Clark

I didn't include the answer to that last calculation:

311*9.81ln(1 + 375/(13 + 6.7)) = 9,145 m/s.

Dr. John Schilling has produced a payload estimation program:

Launch Vehicle Performance Calculator.
http://www.silverbirdastronautics.com/LVperform.html

It gives a range of likely values of the payload. I've found the midpoint of the range it specifies is a reasonably accurate estimate to the actual payload for known rockets.
Input the vacuum values for the thrust in kilonewtons and Isp in seconds. The program takes into account the sea level loss. SpaceX gives the Merlin 1D vacuum thrust as 161,000 lbs and vacuum Isp as 311 s:

FALCON 9 OVERVIEW.
http://www.spacex.com/falcon9.php

For the 9 Merlins this is a thrust of 9*161,000*4.46 = 6,460 kN. Use the default altitude of 185 km and the Cape Canaveral launch site, and a 28.5 degree orbital inclination, to match the Cape's latitude.
Input the dry mass of 13,000 kg and propellant mass of 375,000 kg. Then it gives an estimated 7,564 kg payload mass:

Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Cape Canaveral / KSC
Destination Orbit: 185 x 185 km, 28 deg
Estimated Payload: 7564 kg
95% Confidence Interval: 3766 - 12191 kg

This may be enough to launch the Dragon capsule, depending on the mass of the Launch Abort System(LAS).

Bob Clark

And the fact that Spacex has a second stage should tell you that you are wrong in your assumptions.

 

[DSE]

And the fact that Spacex has a second stage should tell you that you are wrong in your assumptions.

Don't feed the troll. He's done this in various other forums before moving on to new unturned ground. Arguments citing reality mean little if nothing.

 

[XP67_Moonbat]

Ignorance is bliss. And in Clark's case he seems to be quite happy.

 

[RGClark]

And the fact that Spacex has a second stage should tell you that you are wrong in your assumptions.

It is true a multi-stage vehicle can loft more than a single stage. However, there are additional issues such as cost and simplicity. For instance a 3-stage vehicle can loft more than a 2-stage. Despite that SpaceX chose a two-stage design for the Falcon 1 and Falcon 9. But to lift even higher payloads they are going for a three-stage design with the Falcon Heavy.
The base vehicles for the Atlas V and Delta IV are also two stage vehicles. But to lift heavier payloads they add on strap-ons making them three-stage. (Some call parallel staged boosters half-stages, but the principle is you increase the number of stages to increase payload.)
Then SpaceX could use the SSTO version just to launch smaller payloads since you would not need the upper stage for that case.

Bob Clark

 

[XP67_Moonbat]

Are you done?

 

[RGClark]

Elon Musk to Address Mars Society Convention in Pasadena.
posted Jul 20, 2012 10:05 AM by Mars Society - PR [ updated Jul 21,
2012 1:13 PM ]

The Mars Society is very pleased to announce that SpaceX Founder and
CEO Elon Musk will address the 15th Annual International Mars Society
Convention in Pasadena, California, on Saturday, August 4th during the
organization's evening banquet.

http://www.marssociety.org/home/press/announcements/elonmusktoaddressmarssocietyconventioninpasadena

Bob Clark

 

[Byeman]

Elon Musk to Address Mars Society Convention in Pasadena.
posted Jul 20, 2012 10:05 AM by Mars Society - PR [ updated Jul 21,
2012 1:13 PM ]

The Mars Society is very pleased to announce that SpaceX Founder and
CEO Elon Musk will address the 15th Annual International Mars Society
Convention in Pasadena, California, on Saturday, August 4th during the
organization's evening banquet.

http://www.marssociety.org/home/press/announcements/elonmusktoaddressmarssocietyconventioninpasadena

Bob Clark


What does that have to do with SSTO's?

 

[XP67_Moonbat]

I ask again: what does that announcement have to do with SSTO's. Nothing.

 

[RGClark]

Elon Musk to Address Mars Society Convention in Pasadena.
posted Jul 20, 2012 10:05 AM by Mars Society - PR [ updated Jul 21,
2012 1:13 PM ]

The Mars Society is very pleased to announce that SpaceX Founder and
CEO Elon Musk will address the 15th Annual International Mars Society
Convention in Pasadena, California, on Saturday, August 4th during the
organization's evening banquet.

http://www.marssociety.org/home/press/announcements/elonmusktoaddressmarssocietyconventioninpasadena

Bob Clark


What does that have to do with SSTO's?

If I'm right then the new version of the Falcon 9's first stage will have SSTO capability in it's planned configuration, i.e., without even needing engine modifications such as altitude compensation. The only question is how much.
Elon has said the new version will be ready by the end of this year. If it really does have a 30 to 1 mass ratio, then simple application of the rocket equations shows it can be SSTO. Then the question about this capability will necessarily arise then. I was wondering if the question could be posed to him before then.

Bob Clark

 

[Byeman]

You are delusional to think you are right and Spacex over looked this.
And anyways, SSTO's are not viable, no matter what you think

 

[RGClark]

It's a question to ask if they did. And if they did how much payload it could carry. The question about whether it would be useful or not is dependent on how much payload it could carry.
According to the SpaceX web site the new version of the full Falcon 9 will be able to carry 13,150 kg to LEO. Suppose your satellite only weighs 7,000 kg to LEO. Should you pay full price for the full rocket IF the SSTO version could launch it without the extra expense of the upper stage?


Bob Clark

 

[Byeman]

It's a question to ask if they did. And if they did how much payload it could carry. The question about whether it would be useful or not is dependent on how much payload it could carry.

Not enough to matter

 

[RGClark]

Elon Musk to Address Mars Society Convention in Pasadena.
posted Jul 20, 2012 10:05 AM by Mars Society - PR [ updated Jul 21,
2012 1:13 PM ]

The Mars Society is very pleased to announce that SpaceX Founder and
CEO Elon Musk will address the 15th Annual International Mars Society
Convention in Pasadena, California, on Saturday, August 4th during the
organization's evening banquet.

http://www.marssociety.org/home/press/announcements/elonmusktoaddressmarssocietyconventioninpasadena

Elon Musk "Mars Pioneer Award" Acceptance Speech - 15th Annual International Mars Society Convention.
http://www.youtube.com/watch?v=PK0kTcJFnVk


Bob Clark

 

[Byeman]

And what does that have to do with SSTO'S? SSTO'S are not going to help with Mars eloration

 

[RGClark]

And what does that have to do with SSTO'S? SSTO'S are not going to help with Mars eloration

The real reason is that I already posted he was going to speak there, so since the speech was online I thought I'd post that as well.
But I was surprised when I did the calculation how much this possible Falcon 9 v1.1 SSTO could carry from LEO to low Mars orbit. Musk proposes cutting the costs to space by two orders of magnitude by reusability. Then there would be also a dramatic drop in the cost to lift the large amount of propellant to space.
So let's suppose there are propellant depots at LEO. Since Musk proposes a self-sustaining colony on Mars, lets also suppose propellant depots in low Mars orbit for return trips.
Here's a map of delta-v's between Mars/Moon/Earth:

If you add up the delta-v's from low Earth orbit to low Mars orbit you get 6.1 km/s. Now use the same specifications for the Falcon 9 v1.1 first stage as before 13 mT dry mass and 375 mT propellant load. Then you could transport 45 mT from LEO to low Mars orbit:

311*9.81ln(1 + 375/(13 + 45)) = 6,130 m/s.


Bob Clark

 

[RGClark]

With reduced weight of the Merlin 1D while at increased efficiency, the Falcon 9 v1.1 first stage will have SSTO capability. Then ironically Elon is emulating the original purpose of the DC-X program in testing the Grasshopper VTVL stage without realizing it.

Bob Clark

 

[Michel Van]

I had same thought, during watching new Grasshopper test flight on youtube.

But SpaceX has other plans, they want only recovering the First and Second Stage of Falcon rocket
Although a larger Falcon 9 first stage would be interesting reusable SSTO to replace the Falcon 1e.

Sadly SpaceX use Falcon 9/Dragon flight to launch piggyback payload intended for the Falcon 1e.

 

[RGClark]

With reduced weight of the Merlin 1D while at increased efficiency, the Falcon 9 v1.1 first stage will have SSTO capability. Then ironically Elon is emulating the original purpose of the DC-X program in testing the Grasshopper VTVL stage without realizing it.

Bob Clark

Nice article here:

New Mexico space museum volunteers restoring DC-X for exhibit.
by TopSpacer on February 13, 2013 at 3:01 am
http://hobbyspace.com/Blog/?p=591#comment-7550

Bob Clark

 

[RGClark]

The DC-X may yet live again:

Jeff Foust
?@jeff_foust
"DARPA's Pam Melroy: about to kick off Experimental Spaceplane 1 (XS-1)
program, a reusable 1st stage. Industry day early OCtober. #aiaaspace"
https://twitter.com/jeff_foust/status/378177568337166336

The planned suborbital follow on to the DC-X might have been able to
fulfill such a role. And the X-33 even if you replaced the failed composite
tanks with aluminum-lithium could still have served this purpose as a
reusable first stage.

Bob Clark

 

[Arcane]

Here's the DARPA press release announcing the Experimental Spaceplane (XS-1) Program.

Maybe time to move this to Aerospace?

http://www.darpa.mil/NewsEvents/Releases/2013/09/17.aspx

 

[DSE]

XS-1 Proposers Day Announcement

Key technical challenges that will be addressed by the XS-1 program include:

• • A reusable first stage vehicle designed for aircraft-like operations
• • Robust airframe composition leveraging state-of-the-art materials, manufacturing processes, and analysis capabilities
• • Durable, low-maintenance thermal protection systems that provide protection from temperatures and heating rates ranging from orbital vacuum to atmospheric re-entry and hypersonic flight
• • Reusable, long-life, high thrust-to-weight, and affordable propulsion systems
• • Streamlined “clean pad” operations dramatically reducing infrastructure and manpower requirements while enabling flight from a wide range of locations

Additional goals for the XS-1 demonstration program are to:

• • Fly ten times in ten days
• • Fly to Mach 10 at least once
• • Launch a representative payload to orbit at least once

It is anticipated that the program will be divided into three phases:

• • Phase I: Initial Design and Risk Reduction
• • Phase II: Final Design, Fabrication, and Integration Assembly and Test
• • Phase III: Flight Test Campaign

The goals of this meeting are:

1) to familiarize participants with DARPA’s interest in XS-1, and

2) to promote discussion of synergistic capabilities among potential program
participants.

It is our desire to facilitate the formation of strong teams and business
relationships in order to develop comprehensive, quality responses to any potential
DARPA solicitation.

 

[quellish]

The planned suborbital follow on to the DC-X might have been able to
fulfill such a role.

Considering the objective of the SDIO program was to demonstrate technologies for a reusable first stage to loft SDIO targets, I should hope so.

 

[bobbymike]

Nice concept, looks like a nice prompt global strike weapon its launching.

 

[ouroboros]

Yeah, XS-1 with the mach 10 staging requirement and the "clean pad" with aircraft ops requirements smells like a HTHL first stage booster dev program for PGS. It also neatly gets around the problem of having a declared and inspectable PGS launch site to assuage Russia/China that we aren't launching nuke ICBM's, if you were using conventional first stage vertical takeoff boosters.

But none of the space startups will want to mess with mach 10 staging, so this is strictly a big boys only project, which also dovetails neatly into a PGS first stage program.

 

[RanulfC]

Folks, it is not "staging" at Mach-10, the requirement is for it to be ABLE to reach Mach-10 at least once.

"Staging" for an orbital mission would be lower and yes the Mach-10 requirement fits a GSW profile launch. I don't know that anyone has the experiance/know-how to build this as an HTHL vehicle without resorting to trying to justify "SCramjets" for it. My take on the "clean-pad" requirement is probably going to allow for VTHL ops simply because rocket engines will be probably "trade" as the best propulsion solution.

(I'm hoping someone out there brings up the SERJ engine myself but I don't see Air-Breathing as getting any traction unless they turn this into a SCramjet vehicle since that seems to be the only power plant anyone is interested in.)

Randy