Fly Centaur atop Delta IV-H, use as Earth Departure Stage after LEO Rendezvous

[sdsds]

For a mission payload launched to LEO on Atlas V, could a separately launched Centaur (maybe dual-engine) rendezvous with it?  Suppose the Centaur were launched as a passive payload on a Delta-IV Heavy.  Could it reach rendezvous still almost fully loaded with propellant?  After rendezvous, could the Centaur then act as an Earth departure stage for the separately launched mission payload?

Delta IV-Heavy payload to LEO is roughly 20 mT, and that's roughly the wet mass of Centaur....  Is this concept a "no brainer," or is it somehow "brain dead"?

[mmeijeri]

It's been proposed before, by serious people, and it is one of my favourite near term ways to go beyond earth orbit.

[Ben the Space Brit]

IIRC, ULA have already done a study on replacing the Delta-IV upper stages with the Single-Engine Centaur.  Their studies have shown a favorable increase in performance over the DIVUS family.

However, I believe that you are talking about launching the Centaur as a payload, specifically as an EDS for a BEO mission.  For this to work, you would need to solve the following issues:

1) Power supply - How long can Centaur's batteries last? That is the amount of time you have to launch the payload;

    a) Can you fit solar arrays to the Centaur?

2) Rendezvous - How does the Centaur rendezvous with the mission module? (Accepting that Orion would need one for all by the shortest and least-ambitious missions);

3) TOI payloads - Centaur is fairly small as EDS options go.  It is fine for launching a robotic interplanetary probe, but a crewed space probe would be as much as an order of magnitude greater.  Would Centaur be able to push even just an Orion through TOI to any useful destination?

[mmeijeri]

1) Power supply - How long can Centaur's batteries last? That is the amount of time you have to launch the payload;

    a) Can you fit solar arrays to the Centaur?

2) Rendezvous - How does the Centaur rendezvous with the mission module? (Accepting that Orion would need one for all by the shortest and least-ambitious missions);

ULA (or LM before them) proposed an extended duration mission kit for that. You certainly couldn't use the Centaur as is.

3) TOI payloads - Centaur is fairly small as EDS options go.  It is fine for launching a robotic interplanetary probe, but a crewed space probe would be as much as an order of magnitude greater.  Would Centaur be able to push even just an Orion through TOI to any useful destination?

If it's unmanned, without return propellant, yes. Otherwise Orion is too heavy. If you want to do TLI with a Centaur you need a smaller capsule or a bigger Centaur. A Delta IV upper stage would be big enough, and the new Delta IV Heavy with RS-68A or else Atlas V Heavy might barely be able to lift that to orbit. Otherwise you'd need cryogenic propellant transfer.

[Downix]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

[Ben the Space Brit]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

I don't think that anyone has ever done a lateral rendezvous without the assistance of a crewed spacecraft equipped with an RMS.  I'm sure it could be done, but whether the R&D would be cheaper than just building a larger (4- or 6-engine) Centaur-derived EDS is questionable.

[Downix]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

I don't think that anyone has ever done a lateral rendezvous without the assistance of a crewed spacecraft equipped with an RMS.  I'm sure it could be done, but whether the R&D would be cheaper than just building a larger (4- or 6-engine) Centaur-derived EDS is questionable.

The issue with larger units is what will carry it up? 

[mmeijeri]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

ESA was considering something similar, which is not surprising since its cryogenic upper stage is so small. The Mars DRM did something similar, which is not surprising given the large mass it had to put through TMI. But apart from complexity the drawback would be that you would still have to mitigate substantial boil-off issues.

[Ben the Space Brit]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

I don't think that anyone has ever done a lateral rendezvous without the assistance of a crewed spacecraft equipped with an RMS.  I'm sure it could be done, but whether the R&D would be cheaper than just building a larger (4- or 6-engine) Centaur-derived EDS is questionable.

The issue with larger units is what will carry it up? 

A 5.4m-diameter stage could fit on the current Atlas-V and Delta-IV cores without too much trouble.

[Downix]

could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS?  Launch each of them seperately to rendevous up in orbit.

ESA was considering something similar, which is not surprising since its cryogenic upper stage is so small. The Mars DRM did something similar, which is not surprising given the large mass it had to put through TMI. But apart from complexity the drawback would be that you would still have to mitigate substantial boil-off issues.

An option for boil-off is to house a shade around the mounting point of what you are mounting them to.

What if you did not do this in a single go, and you did staged EDS, you use one to push into a large eccentric orbit, then dump the first EDS.  It then meets up with the second EDS, which has burned up more of its fuel to reach the item, and it pushes even more, to get things even more eccentric, where it then meets up with the last EDS, already en route.  A way to get a *bit* more out of the system.

[sdsds]

I believe that you are talking about launching the Centaur as a payload, specifically as an EDS for a BEO mission. 

Yes, and this specific configuration only because of a coincidental similarity:  the  payload to LEO of Delta IV-H is approximately the wet mass of a Centaur.

1) Power supply - How long can Centaur's batteries last?

There was a recent Centaur mission that did some R&D activity after the primary payload was safely separated.  Wasn't that extended mission duration 72 hours or more?

That is the amount of time you have to launch the payload;

Unless the payload launches first and can meet the necessary loiter requirements.  (Understood this is the reverse of the CxP architecture.)  For a payload using hypergolic propellants with a design flight duration measured in weeks, the loiter requirement might be met within existing margins.

2) Rendezvous - How does the Centaur rendezvous with the mission module? (Accepting that Orion would need one for all by the shortest and least-ambitious missions);

Perhaps the mission module could be already at the destination, delivered by a prior launch campaign?

3) TOI payloads - Centaur is fairly small as EDS options go.  It is fine for launching a robotic interplanetary probe, but a crewed space probe would be as much as an order of magnitude greater.  Would Centaur be able to push even just an Orion through TOI to any useful destination?

If it's unmanned, without return propellant, yes. Otherwise Orion is too heavy

So the concept of operations would be the departure stage sending the payload (possibly even including crew) into a nominal "free return" lunar flyby orbit.  The payload would have enough propellant to:

a) in the nominal case, adjust its trajectory and perform an "insertion" burn (or burns) to reach its pre-positioned return propellant.  (Or a pre-positioned return propulsion module.)

b) in the case of a minor departure stage under-burn, supplement the burn to get back on the flyby return trajectory.

c) in the case of a major departure stage under-burn that only reaches a highly elliptical Earth orbit, perform appropriate re-entry burns.

I hope lunar orbit, EML1 and EML2 would be reasonable crewed mission destinations for this architecture.  Is there a hope that dual-launch could be competitive with single-launch architectures for long duration robotic missions?  Does it provide enough more mass to Earth-escape (compared to a single Atlas V 551 or Delta IV-H) to interest the science mission community?  For example would it, in combination with Mars-orbit rendezvous, enable robotic Mars sample return?

[mmeijeri]

An option for boil-off is to house a shade around the mounting point of what you are mounting them to.

That is a good idea, and ULA has been doing some work on that.

What if you did not do this in a single go, and you did staged EDS, you use one to push into a large eccentric orbit, then dump the first EDS.  It then meets up with the second EDS, which has burned up more of its fuel to reach the item, and it pushes even more, to get things even more eccentric, where it then meets up with the last EDS, already en route.  A way to get a *bit* more out of the system.

That could work, but rendez-vous would be more complicated and time-critical. You would also have more van Allen transits, but presumably only the last one would be manned, so that wouldn't be a show stopper.

But rendez-vous in a nearly circular high energy orbit sounds easier. Most likely that orbit would be L1/L2, but MEO or GEO could be used too if the lifeboat scenario is a concern. A bit less efficient, but that might be worth it.

[mmeijeri]

So the concept of operations would be the departure stage sending the payload (possibly even including crew) into a nominal "free return" lunar flyby orbit.  The payload would have enough propellant to:

a) in the nominal case, adjust its trajectory and perform an "insertion" burn (or burns) to reach its pre-positioned return propellant.  (Or a pre-positioned return propulsion module.)

It depends a lot on the size of the stage, the size of the capsule, the choice of staging point and how long the trip is allowed to take. I did a lot of sums on DCSS (Delta IV 5m upper stage, which has a bewildering array of names) and Orion, back when I thought an SDLV was inevitable. With that you could get an Orion to LLO, but not with enough propellant to get back, which seemed too risky. With L1/L2 as a staging point you could get there with enough propellant to both the insertion burn and the TEI. Not with a whole lot of margin, but it looked doable. A slightly bigger stage would be useful.

A Centaur could only get you to L1/L2 on an almost ballistic trajectory, so you wouldn't need an insertion burn. This means the journey takes >=100 days, so this is not suitable for crew. Not being able to bring your return propellant with you also rules it out. But with a smaller capsule a Centaur might work.

I hope lunar orbit, EML1 and EML2 would be reasonable crewed mission destinations for this architecture.

A Lagrange point is all you need. From there everything but LEO can be reached at reasonable cost, even with storable propellant. And since storable propellant transfer is a mature technology, you could easily use refueling at L1/L2. In order to stimulate development of RLVs (and cryogenic depots, maybe even EELV Phase 1) you would want to buy that propellant in LEO, at L1/L2 and also buy transportation services between the two. All that would happen slowly, in the background, without it appearing on the critical path.

  Is there a hope that dual-launch could be competitive with single-launch architectures for long duration robotic missions?  Does it provide enough more mass to Earth-escape (compared to a single Atlas V 551 or Delta IV-H) to interest the science mission community?  For example would it, in combination with Mars-orbit rendezvous, enable robotic Mars sample return?

So far no one has done it, which is not a good sign. In part that may be because it would be too expensive to develop on the budget of a single science mission. Another reason would be that science missions do not now max out the payload size of existing launchers, so there's little point in developing technology that won't be needed for a long time from a science budget.

Of course, once NASA developed the technology for it (or had it developed by industry), it could make it available to science missions as well. An alternative would be refueling at a Lagrange point. Again, NASA would have to pay for the initial development, but once it was available, it could be used by science missions too. In light of current missions not maxing out current launch vehicles, I suspect this would only make sense once things like RLVs had made launching propellant a lot cheaper than it is today.

MSL may be a perfect example. I think the proposal to split it up stems from a lack of funding for developing the spacecraft itself, not because it doesn't fit on a launch vehicle.

[FinalFrontier]

This is an interesting idea.  Sounds a bit like accelerated ACES or mini ACES. Perhaps, in order to make centaur capable of being the EDS all one needs to do is: Add solar wings, add in the ACES low boil off system [could this simply consist of uprated insulation and cold, boil off gas tubes? (only in this case so as to make centaur more capable for the least amount of money)], finally, add the ACES propellant depot sunshade.  In short: mini ACES. This could also fly on jupiter130 as a smaller, cheaper eds

[sdsds]

It makes sense to put some numbers on the proposed Earth departure burn performed by the Centaur.  For the CxP lunar sortie mission, the Orion TLI mass was 20.2 t.  Spacelaunchreport shows the Centaur total mass as 22.83 t.  That's approximately 43 t between the two for m₀.  With a Centaur dry mass  of 2 t that's approximately 22 t for m₁.

Using a Centaur I_sp of 450 s:

450 * 9.8 * ln(43 / 22) = 2,955 m/s of delta-v.

That's nearly the CxP sortie TLI of 3,175 m/s.  The Orion for that mission was to be loaded with propellant for a 1,560 m/s TEI burn from LLO.  It seems like off-loading some of that propellant demonstrates the architecture could "close".

For the return I'm suggesting use of  a full pre-positioned propulsion module (rather than propellant) because rendezvous and docking are fundamental capabilities for Orion.  With Centaur providing the Earth departure burn, all Orion needs to provide is the destination "insertion" burn, and then use its rendezvous and docking capability to dock with a propulsion module that will provide the boost to get home.

[sdsds]

This is an interesting idea.  Sounds a bit like accelerated ACES or mini ACES.

Yes, very much the same idea.  The term "accelerated" here would mean, "using existing stages (or very minor modifications thereof) for the major propulsive maneuvers."  Doing this would allow NASA to focus for the next few years on constructing payloads, principally a "deep space" Orion.

[Robotbeat]

This is an interesting idea.  Sounds a bit like accelerated ACES or mini ACES.

Yes, very much the same idea.  The term "accelerated" here would mean, "using existing stages (or very minor modifications thereof) for the major propulsive maneuvers."  Doing this would allow NASA to focus for the next few years on constructing payloads, principally a "deep space" Orion.

I'm a fan of this idea. Existing stages means lower costs (unless you have a LOT of money to devote to exploration, in which case an exploration-focused stage can make sense, maybe) and lower time for development.

[mmeijeri]

On the performance calculations: I'm getting about 17.5mT through TLI. You also have to take the mass of a docking mechanism and an extended duration mission kit into account. That might be enough to do L1/L2 insertion as well, even without the capacity of a Delta upper stage. I'd be uneasy with not having return propellant. A smaller capsule sounds like a better idea to me.

[FinalFrontier]

Ok question 2: How soon can the "mini ACES" be ready? The sooner the better. Also I would suggest using an avionics pacakge that is easily compatible with both EELV and SDHLV. That way this could fly on whatever rocket is availble.

[FinalFrontier]

On the performance calculations: I'm getting about 17.5mT through TLI. You also have to take the mass of a docking mechanism and an extended duration mission kit into account. That might be enough to do L1/L2 insertion as well, even without the capacity of a Delta upper stage. I'd be uneasy with not having return propellant. A smaller capsule sounds like a better idea to me.

I do not like the idea of a smaller capsule............what about making centaur longer, in addition to adding solar wings, sunshades, low boiloff insulation/cold gas tubing ect?? I'm thinking mini ACES 71. Add second engine or switch to RL-10-B2 for more thrust.

Jim, would really like your input on the "mini ACES/ EDS centaur" idea.