LV Design to launch full-size DreamChaser on Strato-Launch

[Todd Martin]

It would be helpful for SNC & Stratolaunch if the Stratolaunch system was powerful enough to launch a full scale Dreamchaser.  A full size DC would be cheaper to complete development than working on a scale-down.  A full size DC could compete on commercial crew services to ISS and compete on ISS cargo.  A Stratolaunch system which could loft a full size DC would also be more capable in competing on commercial satellite business.

I've done some work on rocket design to see if this is feasible.  Below, I lay out the launch vehicle (LV) which I believe could do the job.

GLOW (Gross Liftoff Weight):  227,273 kg (500,000 lbs).
 
1st Stage: 
  3 J2X engines with nozzles optimized for ignition at 30,000 feet.  ISP:  419 seconds, total thrust 3683KN
  Dry Mass 22,900kg
  Prop mass 169883kg
2nd Stage:  Delta IV 2nd stage with 4 meter fairing
  2 RL10B engines:  ISP:  470 seconds, total thrust 220KN
  Dry Mass 2780kg
  Prop mass 20410kg
Dreamchaser (no fairing):  Mass = 11,300kg

Length of Launch Vehicle:  100 feet (1st stage) + 40 feet (2nd stage) + 30 feet (DC) = 170 feet.

Stratolaunch aircraft provides 250 meters/sec initial velocity.  In addition, the LV is launched at a 15 degree angle of attack instead of vertically, which provides another 600 meters/sec advantage.  Finally, StratoLaunch allows for launch closer to the equator (by 1500 km).

The question is whether Stratolaunch can launch a full-size DC with the appropriate LV mounted to its belly.  If so, what would be the best design to accomplish this requirement.  I've made my best shot at it, I invite others to review & comment.  Thanks!

[dror]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

[Todd Martin]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

That's a good question.  From what I understand, there are 2 issues which must be considered.  First, are the engines able to be lit while in flight?  How much boil-off of the cryogenic fuel will take place before LV ignition?

For the LV proposal, I selected the J2-X engine.  The J2-X can be lit while in flight, aka "Air-start"; it also has a higher ISP than the RS-68 engine or RS-68A engine as used on the Delta IV.  The SSME would have an even higher IPS, but the SSME is not an "Air-start" engine.

As for Boil-off, the rate depends on the insulation, tank diameter, and time.  It is an issue which would need careful analysis.  I can think of a few ways to mitigate boil-off, but at this time I am really interested in knowing whether the concept is feasible.

[Rocket Science]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

That's a good question.  From what I understand, there are 2 issues which must be considered.  First, are the engines able to be lit while in flight?  How much boil-off of the cryogenic fuel will take place before LV ignition?

For the LV proposal, I selected the J2-X engine.  The J2-X can be lit while in flight, aka "Air-start"; it also has a higher ISP than the RS-68 engine or RS-68A engine as used on the Delta IV.  The SSME would have an even higher IPS, but the SSME is not an "Air-start" engine.

As for Boil-off, the rate depends on the insulation, tank diameter, and time.  It is an issue which would need careful analysis.  I can think of a few ways to mitigate boil-off, but at this time I am really interested in knowing whether the concept is feasible.

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

[jongoff]

As for Boil-off, the rate depends on the insulation, tank diameter, and time.  It is an issue which would need careful analysis.  I can think of a few ways to mitigate boil-off, but at this time I am really interested in knowing whether the concept is feasible.

It's probably possible to make this work from a boiloff standpoint using something like what the Quest Thermal guys are developing (http://www.questthermal.com/products/launch-vehicle-mli). Apologies to those who've already seen me comment on this before. But basically they have a way of making a lightweight vacuum-jacketed MLI insulation solution that can work on the outside of launch vehicles. Cuts the heat leak way down, and could theoretically be combined with a vapor cooled shield of some sort (Quest did some experiments in this direction previously) to take what boiloff you do get, and use it to intercept heat leaking into the tanks. If pure insulation isn't enough you could have either a small topping tank that you disconnect shortly before launch (it can be insulated a ton better), or subcool one or both propellants. Lots of ways to do this, but the first key is good insulation.

I think a LOX/LH2 air-launch is doable, though I'm not endorsing (or dissing) this specific approach.

~Jon

[jongoff]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

That's a good question.  From what I understand, there are 2 issues which must be considered.  First, are the engines able to be lit while in flight?  How much boil-off of the cryogenic fuel will take place before LV ignition?

For the LV proposal, I selected the J2-X engine.  The J2-X can be lit while in flight, aka "Air-start"; it also has a higher ISP than the RS-68 engine or RS-68A engine as used on the Delta IV.  The SSME would have an even higher IPS, but the SSME is not an "Air-start" engine.

As for Boil-off, the rate depends on the insulation, tank diameter, and time.  It is an issue which would need careful analysis.  I can think of a few ways to mitigate boil-off, but at this time I am really interested in knowing whether the concept is feasible.

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

With air-launch, it's a lot easier to get booster RTLS without having to pay a big penalty: http://selenianboondocks.com/2008/09/orbital-access-methodologies-part-vi-air-launched-glideforward-tsto/

You just have your drop point be up-range of your landing point, so your booster glides forward to somewhere near the airstrip you took off from (after factoring in any retro-burns for deceleration, etc). As for how to do the landing, you could have some dedicated landing engines, and land either vertically or horizontally. Or you could use wings, or helicopter blades, or possibly even mid-air recovery. Lots of options, though my personal faves in this case would be horizontal rocket powered landing, or helicopter landing.

How heavy would the first stage be dry?

~Jon

[Todd Martin]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

How heavy would the first stage be dry?

~Jon

Dry mass of the 1st stage would be 22,900 kg (50,380 lbs) with a 5 meter diameter tank.

[Comga]

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

With air-launch, it's a lot easier to get booster RTLS without having to pay a big penalty: http://selenianboondocks.com/2008/09/orbital-access-methodologies-part-vi-air-launched-glideforward-tsto/

You just have your drop point be up-range of your landing point, so your booster glides forward to somewhere near the airstrip you took off from (after factoring in any retro-burns for deceleration, etc). As for how to do the landing, you could have some dedicated landing engines, and land either vertically or horizontally. Or you could use wings, or helicopter blades, or possibly even mid-air recovery. Lots of options, though my personal faves in this case would be horizontal rocket powered landing, or helicopter landing.
~Jon

This isn't a really serious disucssion, but for it, Jon has a good point, which we knew he would bring up again.  It answers the question "What Would Elon Do?" in that it puts affordability over performance.
Rather than fly to the equator to gain some percentage in payload to orbit (Think Sea Launch sailing two giant ships to the equator) the launch is optimized for economy, in this case recovery of expensive hardware.

Then you have to work on the cost of two RL-10s.  If we are discussing "pie in the sky" you might want to hypothesize another hydrolox engine, like from Blue Origin or Xcor.

[jongoff]

Dry mass of the 1st stage would be 22,900 kg (50,380 lbs) with a 5 meter diameter tank.

Yeah, I saw that after I posted the comment. 50klb is fairly heavy. You'd probably be talking about 2-4x RL-10 class engines for landing.

~Jon

[jongoff]

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

With air-launch, it's a lot easier to get booster RTLS without having to pay a big penalty: http://selenianboondocks.com/2008/09/orbital-access-methodologies-part-vi-air-launched-glideforward-tsto/

You just have your drop point be up-range of your landing point, so your booster glides forward to somewhere near the airstrip you took off from (after factoring in any retro-burns for deceleration, etc). As for how to do the landing, you could have some dedicated landing engines, and land either vertically or horizontally. Or you could use wings, or helicopter blades, or possibly even mid-air recovery. Lots of options, though my personal faves in this case would be horizontal rocket powered landing, or helicopter landing.
~Jon

This isn't a really serious disucssion, but for it, Jon has a good point, which we knew he would bring up again.

Thanks, I think. :-)

Re: the 2x RL-10 engines, those aren't a showstopper if you're not recovering them, but going either with XCOR or Blue Origin engines or upper stage recovery/reuse (working on it!) would definitely help from an economics standpoint.

But the underlying concept even without reuse wouldn't be a non-starter, though I don't know if it'd be any cheaper than say an Atlas V. Especially once you factor in the development costs.

~Jon

[Todd Martin]

An RL10-B has a thrust of 110KN in vacuum, so you would need at least 3 to provide 1G of thrust to 22,900kg of dry mass + some prop at the ground.

Alternatively, a J2X engine can be throttled down to 82%.  If a center placed J2X was given a ground level type nozzle, it could do a vertical landing burn via "hover slam" at around 4 G's.

According to this link, http://depletedcranium.com/we-need-a-new-cheaper-upper-stage-engine/ the price of an RL10 is $38 Million while a J2-X would be $25 Million each.  So, my configuration for the LV of 3 J2X & 2 RL10's has a total engine cost of $151 million which is perhaps why a hydrolox concept is not being pursued for Stratolaunch.  The Atlas V / CST-100 combo will be using 2 RL10's also, so it isn't completely out of the realm of possibility. 

It seems to me that if commercial price pressures were to be brought to bear on hydrolox engines, these prices could be substantially reduced and become competitive with kerolox engines.  If Stratolaunch went this route, such savings could be realized.

 

 

[Patchouli]

An RL10-B has a thrust of 110KN in vacuum, so you would need at least 3 to provide 1G of thrust to 22,900kg of dry mass + some prop at the ground.

Alternatively, a J2X engine can be throttled down to 82%.  If a center placed J2X was given a ground level type nozzle, it could do a vertical landing burn via "hover slam" at around 4 G's.

According to this link, http://depletedcranium.com/we-need-a-new-cheaper-upper-stage-engine/ the price of an RL10 is $38 Million while a J2-X would be $25 Million each.  So, my configuration for the LV of 3 J2X & 2 RL10's has a total engine cost of $151 million which is perhaps why a hydrolox concept is not being pursued for Stratolaunch.  The Atlas V / CST-100 combo will be using 2 RL10's also, so it isn't completely out of the realm of possibility. 

It seems to me that if commercial price pressures were to be brought to bear on hydrolox engines, these prices could be substantially reduced and become competitive with kerolox engines.  If Stratolaunch went this route, such savings could be realized.

 

 

Replace the three RL-10s with a single BE-3 the ISP is lower but it's thrust is much higher so you only need one and it's a lot cheaper.
Though on the cost of the J-2X 25 million was with a low production for Ares would have needed.
If it was used in a rocket that flew more often it might be cheaper.

As for return  the stage already has wings and is launched horizontally  here glide back sort of landing and using landing gear may be more idea then transitioning the stage to vertical and landing it.

I wonder could the hybrids in DC be replaced with two Chase-10 or Xcor methane engines allowing it to effectively be it's own upper stage?

[ChrisWilson68]

Replace the three RL-10s with a single BE-3 the ISP is lower but it's thrust is much higher so you only need one and it's a lot cheaper.
Though on the cost of the J-2X 25 million was with a low production for Ares would have needed.
If it was used in a rocket that flew more often it might be cheaper.
I wonder could the hybrids in DC be replaced with two Chase-10 or Xcor methane engines allowing it to effectively be it's own upper stage?

Then you'd have to take your upper stage tanking through re-entry and landing.  There's no room in the current DC design for that.

[Robotbeat]

For air-launch, hydrogen is pretty dang optimal. The Isp advantage makes a big difference since you're limited strongly by lift-off-mass (or, more pedantically, slung mass), more so than a ground launch where you can compensate with more thrust or a couple more solids without much trouble.

[Oli]

ISP:  419 seconds

Shouldn't that be more?

Is it even possible to carry and launch a cryogenic vehicle from this platform?

That's a good question.  From what I understand, there are 2 issues which must be considered.  First, are the engines able to be lit while in flight?  How much boil-off of the cryogenic fuel will take place before LV ignition?

For the LV proposal, I selected the J2-X engine.  The J2-X can be lit while in flight, aka "Air-start"; it also has a higher ISP than the RS-68 engine or RS-68A engine as used on the Delta IV.  The SSME would have an even higher IPS, but the SSME is not an "Air-start" engine.

As for Boil-off, the rate depends on the insulation, tank diameter, and time.  It is an issue which would need careful analysis.  I can think of a few ways to mitigate boil-off, but at this time I am really interested in knowing whether the concept is feasible.

Those J2-X engines are pretty expensive to throw away, it would make more sense if this were a flyback stage...

With air-launch, it's a lot easier to get booster RTLS without having to pay a big penalty: http://selenianboondocks.com/2008/09/orbital-access-methodologies-part-vi-air-launched-glideforward-tsto/

Booster flyback doesn't need much fuel though.

However for point-to-point transport air-launch might be very interesting...

[Patchouli]

Replace the three RL-10s with a single BE-3 the ISP is lower but it's thrust is much higher so you only need one and it's a lot cheaper.
Though on the cost of the J-2X 25 million was with a low production for Ares would have needed.
If it was used in a rocket that flew more often it might be cheaper.
I wonder could the hybrids in DC be replaced with two Chase-10 or Xcor methane engines allowing it to effectively be it's own upper stage?

Then you'd have to take your upper stage tanking through re-entry and landing.  There's no room in the current DC design for that.

I was mostly thinking in acting as a third stage with DC it's self supplying  about 1000M/sec  of the delta V vs replacing the second stage to compensate for the lower ISP of the BE-3 vs RL-10.
Though advanced hybrids or even really good hypergolics may have enough performance to make this unnecessary.

To eliminate the second stage you could make use of drop tanks like the Soviet MAKS concept.

In that case the drop tank would be much smaller maybe around 1/3rd the size of the one on MAKS esp if the Chase-10 is used instead of the RL-10 for the integrated engine since methane is more dense.

It's kinda backwards of what would be ideal as the lower ISP propellant should be in the first stage.
Though this arrangement is not unlike the Antares rocket and the Delta II which have a higher performance first stage then their second stages.

[TomH]

Is it even possible to carry and launch a cryogenic vehicle from this platform?

That's a good question.  From what I understand, there are 2 issues which must be considered.

Carry is the optimal word to me. In my mind's eye, this is what I see. You suspend that thing horizontally from the single suspension point. You then begin loading liquid prop. The fragile fuselage begins to sag at both ends from the weight. Well before the tanks are full, the thing just rips apart. Even if you manage to avoid that, you take off and the vibrational harmonics finish the job.

[Todd Martin]

Just a couple points:

I estimated 419 ISP for the J2X rather than the 448 ISP listed at vacuum since the engine will light around 30,000 feet.  At that altitude, air pressure is about 25% sea level.

The Stratolaunch carrier aircraft is designed to support about 500,000 lbs.  In the photos, the attachment is along the central wing which is ~ 26 feet wide.  If the moment arm becomes un-manageable due to LV length, then a 2nd attachment point further toward the tail could be made but the aircraft designers have not felt that to be necessary so far.

[TomH]

Just a couple points:

I estimated 419 ISP for the J2X rather than the 448 ISP listed at vacuum since the engine will light around 30,000 feet.  At that altitude, air pressure is about 25% sea level.

The Stratolaunch carrier aircraft is designed to support about 500,000 lbs.  In the photos, the attachment is along the central wing which is ~ 26 feet wide.  If the moment arm becomes un-manageable due to LV length, then a 2nd attachment point further toward the tail could be made but the aircraft designers have not felt that to be necessary so far.

It's not the weight the attachment point can carry, it's whether or not a super thin skinned fuselage can support the leveraged weight of the prop. I did not say the attachment point would fail. I am suggesting the fuselage itself would rip apart when suspended from the center horizontally.

[ChrisWilson68]

Replace the three RL-10s with a single BE-3 the ISP is lower but it's thrust is much higher so you only need one and it's a lot cheaper.
Though on the cost of the J-2X 25 million was with a low production for Ares would have needed.
If it was used in a rocket that flew more often it might be cheaper.
I wonder could the hybrids in DC be replaced with two Chase-10 or Xcor methane engines allowing it to effectively be it's own upper stage?

Then you'd have to take your upper stage tanking through re-entry and landing.  There's no room in the current DC design for that.

I was mostly thinking in acting as a third stage with DC it's self supplying  about 1000M/sec  of the delta V vs replacing the second stage to compensate for the lower ISP of the BE-3 vs RL-10.
Though advanced hybrids or even really good hypergolics may have enough performance to make this unnecessary.

Ah, thanks for the clarification.  I thought you meant it would be the second stage.

To eliminate the second stage you could make use of drop tanks like the Soviet MAKS concept.

In that case the drop tank would be much smaller maybe around 1/3rd the size of the one on MAKS esp if the Chase-10 is used instead of the RL-10 for the integrated engine since methane is more dense.

It's kinda backwards of what would be ideal as the lower ISP propellant should be in the first stage.
Though this arrangement is not unlike the Antares rocket and the Delta II which have a higher performance first stage then their second stages.

That's not entirely unlike what the shuttle did, so it certainly can be done.  There is some appeal to dropping just the tank and bringing back the engines.