SpaceX to NASA quote : simplified mission architecture : Technical discussion

[Vultur]

I think that has been said at some point, but the recent Moon and Beyond" update refers to "Raptor lunar landing throttle test demonstrating a representative thrust profile that would allow Starship to land on the lunar surface".

That looks to me like SpaceX is still hoping to land on the Moon (not just Mars) with Raptors, and may be trying to demonstrate this at least partly with the intent to offer "no landing thrusters needed" to NASA as a potential simplification.

It's absolutely a requirement to use Raptors to land on the Moon.  What's at issue is whether to use Raptors for the last hundred meters or so.  But there's still a throttle profile that's required.

Even if you're using thrusters, you need the Raptors to deliver the HLS to a specific height with a specific downward velocity.  If the velocity is too low, the thrusters have to use a lot of extra prop, and if they get close to running out, that's an abort.  If the velocity is too high, then the thrusters' thrust may not be adequate to do a safe hoverslam, and that's also an abort--or a crash.

That makes sense.

So do you think SpaceX has given up on Raptor-only landing?

[TheRadicalModerate]

So do you think SpaceX has given up on Raptor-only landing?

I don't know.  There were methox or methalox thruster tests at McGregor a couple of years ago but, AFAIK, nothing since then.  That doesn't sound like something that's going into HLS.  So that seems to leave two possibilities:

1) They're almost sure that Raptor landing will work.  I don't know how they would have come to that conclusion, so I suspect it's not the answer.

2) They're planning on using SuperDracos for landing and ascent,¹ as a temporary measure.  This would require fixing the SD's problem with backflow through the check valves.  (For the D2, the check valves have been replaced with a burst disc, which makes the system good for only one burn.  That's adequate for D2 launch escape, but not for what would have to happen with Starship.)

SDs would be a pain, and they won't work for a reusable HLS (no way to refuel them and replenish their pressurant), but they're well-understood and, oddly, about the right thrust for Starship's purposes.  But they're pressure-fed, and they'd need quite a bit more prop.²

I view the thruster situation as a non-trivial source of schedule risk.

____________
¹Raptors can be used for trajectory correction maneuvers, at least in theory.  However, I'm skeptical that they'd be particularly accurate doing burns for 1-5m/s delta-v.  I'd expect thrusters to fill that role, as well as for coarse attitude control, where cold gas would not be very responsive in the control system.  But this may be one of those "best part is no part" decisions on SpaceX's part, while they wait for some data from the refueling tests, which should exercise both of these functions.

²For your dancing and dining pleasure, here's a spreadsheet that shows how much prop is needed for various combinations of Raptor shutdown height, shutdown velocity, and startup height during ascent.  Note!  If you copy it to play with it, it needs iterative calculation turned on, because the prop needed to land isn't factored into the wet mass that's entered as a parameter.

Note that thruster prop mass gets really out of hand if you make the shutdown happen too high, or the shutdown velocity too small.  For comparison, SD prop capacity is about 1.4t on the D2.

[Brigantine]

Now that there is wider discussion of Orion-on-the-nose, specifically LEO to LLO.
Since the rumour is that it's related to simplified mission architecture, I'll post here. Maybe I missed some discussion elsewhere.

Including how much "eyeballs-out" acceleration Orion and the docking port (and now the solar panels) can handle and engine configurations to propel Starship at said reduced acceleration levels. There was a fair point on the latest Flame Trench about how using a single sea-level raptor gives you slightly off-axis thrust, meaning the docking port is also carrying some loads in shear and bending. (meaning the combined load is more limiting than pure axial compression would be)

Some points I felt were missing:

1) During the TLI burn Orion/ESM's mass is virtually constant, so a constant (limiting) force through the docking port corresponds to a constant acceleration of Starship, not a fixed thrust setting. The thrust setting/engine configuration would start out moderate and then taper down.

2) The rocket-equation savings from HLS not needing to ascend to NRHO are material. Orion doesn't subtract 1-for-1 from payload mass, and there is margin freed up for lower ISP etc. in the TLI burn.
(OR to reduce the scope of or eliminate the final tanking orbit and/or reduce number of tanker flights)
_{EDIT: final tanking orbit is some flavour of LEO if Orion is only launched to "LEO", so maybe that's a lot of margin used up already, compared to the hypothetically up to 100,000km+ FTO. Perhaps this is a modest-payload proposal after all, depending on Starship performance. Although you guys are all optimistic about Starship performance anyway.}

3) Depending on how the landing engines are implemented, (if they use mains prop directly or indirectly) they may have some utility in the TLI burn. Either on their own once a single min-throttle RSL is too much, or potentially in combination with a subset of raptors  (i.e. single or 2 throttled RSLs) for roll-control and/or (partially?) balancing the off-axis thrust.
(If it's superdracos then forget it. In the extreme case this turns into "use the 'shunting' engines to finish the landing")

I'd love to see SLS sans 2nd stage used to do the former job of Ares I, while Starship does the former job of Ares V. If SLS needs the cadence just to keep the program alive then it should be fine if they spend some launches on low-performance payload lifts, while SLS sort out their "standardized upper stage" and future plans.

Some questions:

A) Is there any way they could do a maneuver with the hatch open between docked vehicles? I'm thinking about the loads that could be carried by cabin pressure through the hatch, but I presume safety considerations (rapid unplanned depressurization) would preclude it.

B) Re Orion's solar panels, if that is the short straw in terms of acceleration, could their deployment be postponed until after TLI? Or can they be re-stowed after checkouts? While HLS could provide power to Orion while docked, You probably wouldn't want to rely on that once you're committed to at least a free-return. What is the most X-axis-aligned position they can take? What's their range of movement?

[hektor]

I'm still quite surprised that the process is treated as a straightforward LEO-to-LLO (Low Earth Orbit to Low Lunar Orbit) trajectory for Starship HLS. Starship actually involves two propellant aggregation stages: primary refueling in LEO (where multiple tanker flights fill a depot or the HLS vehicle itself), followed by a secondary top-off in a highly elliptical Earth orbit (HEO or HEEO, often called the Final Tanking Orbit or FTO).

It doesn't make much sense to depart directly from the initial LEO aggregation point.

Therefore Orion should meet Starship in Final Tanking Orbit or FTO

[crandles57]

I'm still quite surprised that the process is treated as a straightforward LEO-to-LLO (Low Earth Orbit to Low Lunar Orbit) trajectory for Starship HLS. Starship actually involves two propellant aggregation stages: primary refueling in LEO (where multiple tanker flights fill a depot or the HLS vehicle itself), followed by a secondary top-off in a highly elliptical Earth orbit (HEO or HEEO, often called the Final Tanking Orbit or FTO).

It doesn't make much sense to depart directly from the initial LEO aggregation point.

Therefore Orion should meet Starship in Final Tanking Orbit or FTO

It doesn't make much sense to have Orion docked to Starship before or during refuelling. However does this preclude some adjustment to the orbit after final tanking and before docking? Thinking something like

Tankers/depot fill HLS in 200km circular
Final tanking orbit 200km * 10,000km
Adjust to 180km * 15,000km before docking with Orion at this more highly ellipical orbit and TLI from there.

The more energetic the orbit that Orion joins at, the less the HLS has to accelerate Orion, the better re fuel consumption? This goes higher into outer VAB which might be less ideal but Orion has plenty of radiation shielding?

 

[TomH]

Now that there is wider discussion of Orion-on-the-nose, specifically LEO to LLO.
Since the rumour is that it's related to simplified mission architecture, I'll post here. Maybe I missed some discussion elsewhere.

https://forum.nasaspaceflight.com/index.php?topic=64605.0

I'm still quite surprised that the process is treated as a straightforward LEO-to-LLO (Low Earth Orbit to Low Lunar Orbit) trajectory for Starship HLS. Starship actually involves two propellant aggregation stages: primary refueling in LEO (where multiple tanker flights fill a depot or the HLS vehicle itself), followed by a secondary top-off in a highly elliptical Earth orbit (HEO or HEEO, often called the Final Tanking Orbit or FTO).

It doesn't make much sense to depart directly from the initial LEO aggregation point.

Therefore Orion should meet Starship in Final Tanking Orbit or FTO

It doesn't make much sense to have Orion docked to Starship before or during refuelling. However does this preclude some adjustment to the orbit after final tanking and before docking? Thinking something like

Tankers/depot fill HLS in 200km circular
Final tanking orbit 200km * 10,000km
Adjust to 180km * 15,000km before docking with Orion at this more highly ellipical orbit and TLI from there.

The more energetic the orbit that Orion joins at, the less the HLS has to accelerate Orion, the better re fuel consumption? This goes higher into outer VAB which might be less ideal but Orion has plenty of radiation shielding?

The HLS could be repropped in LEO. Then a pusher version of SS that has also be repropped could dock from behind. Finally, Orion docks nose to nose with HLS. Eyeballs out inside of Orion during TLI is one architecture. Crew transfer to HLS prior to TLI for eyeballs in TLI is another. The pusher stage performs TLI, then returns to LEO. The HLS performs LOI, landing, and ascent burns

[crandles57]

The HLS could be repropped in LEO. Then a pusher version of SS that has also be repropped could dock from behind. Finally, Orion docks nose to nose with HLS. Eyeballs out inside of Orion during TLI is one architecture. Crew transfer to HLS prior to TLI for eyeballs in TLI is another. The pusher stage performs TLI, then returns to LEO. The HLS performs LOI, landing, and ascent burns

That is a nice possibility with only one trip through VAB if such a pusher docking mechanism has been developed.

If it hasn't yet been developed then does developing it fit the 'simplified' description of the mission and allow it to be done rapidly?

[DanClemmensen]

The HLS could be repropped in LEO. Then a pusher version of SS that has also be repropped could dock from behind. Finally, Orion docks nose to nose with HLS. Eyeballs out inside of Orion during TLI is one architecture. Crew transfer to HLS prior to TLI for eyeballs in TLI is another. The pusher stage performs TLI, then returns to LEO. The HLS performs LOI, landing, and ascent burns

That is a nice possibility with only one trip through VAB if such a pusher docking mechanism has been developed.

If it hasn't yet been developed then does developing it fit the 'simplified' description of the mission and allow it to be done rapidly?

A pusher docking mechanism would be one way to dock a Depot to an SS. The Depot would have a nose that looks a lot like A Booster's hot-stage truss but with extendable struts instead of fixed-length struts. This converts the truss into a Stewart platform and provides a 6DOF zero-force docking mechanism similar to the IDSS soft-docking mechanism.  Such a Depot would need a separate "SQD" on an arm to actually transfer propellant for its primary function, but it can act as a pusher without actually transferring propellant.

As you say, if SpaceX is not using this approach for Depot, then this is a big new development. We have no evidence that they are even considering this approach.

[crandles57]

Such a Depot would need a separate "SQD" on an arm to actually transfer propellant for its primary function, but it can act as a pusher without actually transferring propellant.

That extra sqd arm sounds like another big extra development. Isn't it easier to have both the normal side by side docking for propellant transfers (perhaps receive only for a pusher) as well as the in line docking solely for pushing?

Just the in line docking seems a big enough development where we know nothing about any such development having been done that I doubt it being the plan for a race to land humans on the moon.

[maquinsa]

I had an idea for an architecture a while ago but I did't see this forum I don't know if it has been mentioned before but why not:

- launch HLS into LEO
- refuel HLS
- launch Dragon on Falcon 9 to HLS
- HLS pushes itself and the docked dragon to the moon (TLI)
- Dragon decouples in Low Lunar Orbit
- HLS lands
- surface OPS
- HLS to LLO and docks with Dragon
- Send lunar return starship (no cargo, no crew quarters, just a docking port) to LLO (With its own refueling process)
- HLS decouples from Dragon
- Dragon docks too the lunar return starship stage
- Dragon gets pushed back to earth

You need two starships (and their refuelling) , a falcon 9 with dragon and a lot of docking maneuvers...

Doing the numbers it is possible and the second starship barely needs any refueling. If HLS is light enough it might be possible to do it with only HLS as LLO to earth entry is only 800 m/s

[DanClemmensen]

I had an idea for an architecture a while ago but I did't see this forum I don't know if it has been mentioned before but why not:

- launch HLS into LEO
- refuel HLS
- launch Dragon on Falcon 9 to HLS
- HLS pushes itself and the docked dragon to the moon (TLI)
- Dragon decouples in Low Lunar Orbit
- HLS lands
- surface OPS
- HLS to LLO and docks with Dragon
- Send lunar return starship (no cargo, no crew quarters, just a docking port) to LLO (With its own refueling process)
- HLS decouples from Dragon
- Dragon docks too the lunar return starship stage
- Dragon gets pushed back to earth

You need two starships (and their refuelling) , a falcon 9 with dragon and a lot of docking maneuvers...

Doing the numbers it is possible and the second starship barely needs any refueling. If HLS is light enough it might be possible to do it with only HLS as LLO to earth entry is only 800 m/s

You will need to upgrade Dragon for BLEO operation, among other considerations.

Please see this Dragon-on-the-nose post by TheRadicalModerate at
   https://forum.nasaspaceflight.com/index.php?topic=59662.msg2533792#msg2533792
along with further discussion there.

[TomH]

I had an idea for an architecture a while ago but I did't see this forum I don't know if it has been mentioned before
- launch Dragon on Falcon 9 to HLS
- HLS pushes itself and the docked dragon to the moon (TLI)

It has been mentioned ad infinitum.

D2 is not a lunar capable capsule. It does not have the shielding for Van Allen belts. It does not have the capacity for food, oxygen, maneuvering propellant, etc.

[Robotbeat]

All those things are pretty easy. SpaceX even has a trunk propulsion system they could add. But the heatshield is the big one and would need a test flight to qualify

[maquinsa]

I had an idea for an architecture a while ago but I did't see this forum I don't know if it has been mentioned before
- launch Dragon on Falcon 9 to HLS
- HLS pushes itself and the docked dragon to the moon (TLI)

It has been mentioned ad infinitum.

D2 is not a lunar capable capsule. It does not have the shielding for Van Allen belts. It does not have the capacity for food, oxygen, maneuvering propellant, etc.

I see, i should have researched more, I haven't been reading this topic but there are a lot of interesting ideas!