SpaceX Falcon Heavy : PPE/HALO : LC-39A : NLT September 2027

[Robotbeat]

Here's an image GAO says comes from the contractors, showing the co-manifested payload under the fairing. Since PPE is on top, couldn't they squeeze a STAR-48V motor into the upper conical section of the fairing?

NASA (in LSP-PLN-324.01 Revision C) specifically allows, "final stages (exclusively used for orbit circularization or escape)" to be added to a LV, without requiring recertification.

Just use a different trajectory or refuel the PPE instead of kludging a stage in there.

[Jim]

Just use a different trajectory

Can't.

[sdsds]

Here's an image GAO says comes from the contractors, showing the co-manifested payload under the fairing. Since PPE is on top, couldn't they squeeze a STAR-48V motor into the upper conical section of the fairing?

NASA (in LSP-PLN-324.01 Revision C) specifically allows, "final stages (exclusively used for orbit circularization or escape)" to be added to a LV, without requiring recertification.

It would be part of the spacecraft and not launch vehicle.  [...]

They don't have the mass allowance for it.

Yes, and yes, both valid points. Plus there might well be center-of-gravity concerns with a solid motor way up on top of a wobbly payload stack.

The LSP elvperf calculator does seem to put a hard limit on separated payload mass for FH at 15545 kg. But the SpaceX payload user guide doesn't seem to match that. It seems to put the payload limit up somewhere just shy of 19000 kg. Is there a reason for the difference?

[Robotbeat]

Yes, LSP (and the user’s guide to some extent) are conservative and years old. They also may require mods to the payload adapter. Allowing greater performance may require more engineering analysis to prove sufficient margins, etc.

[LouScheffer]

So what could SpaceX practically do to increase payload, assuming the FH is already fully expendable?

(a) Burn the second stage to depletion.  In the very worst case (-3 sigma) this does not help at all, but it almost always provides some extra delta-V.
(b) Burn the side boosters to depletion.  They may already do this on expendable FH missions.  They may need to stop when the first booster is empty, but maybe not - solid side boosters don't burn out at the exact same time, either.
(c) Build a custom (lighter) payload adapter designed exactly to this mission's specification, if it's not using one already.
(d) Review the test results from testing many second stages, and pick only the "hottest" engine.  Also theoretically possible with first stages, but they average over more engines so it won't help as much, and is much harder logistically.
(e) Set tighter weather constraints, such as lower maximum temperature (for colder and denser fuel), favorable winds, etc.
(f) Maybe push the first stage LOX load to later in the count, as they do the second stage.
(g) Remove recovery hardware from fairings.

Any other suggestions? 

[soltasto]

So what could SpaceX practically do to increase payload, assuming the FH is already fully expendable?

Any other suggestions?

If the payload allows it, they could drop the fairings sooner like they do on Starlink missions. However PPE and HALO most likely cannot be exposed earlier to the high atmosphere so that is likely impossible.

SpaceX may also play with thrust limits a bit, in two ways:
1) Higher nominal thrust (they seem to have done this lately, maybe thrust can be increased even more if the engines only have to be used once
2) Higher G loads near MECO and SECO (less throttling) and tighter max-Q bucket

[Jim]

Yes, LSP (and the user’s guide to some extent) are conservative and years old. They also may require mods to the payload adapter. Allowing greater performance may require more engineering analysis to prove sufficient margins, etc.

Already using a unique adapter

[Jim]

(g) Remove recovery hardware from fairings.

New longer fairing and non recovery already factored in

[Comga]

So what could SpaceX practically do to increase payload, assuming the FH is already fully expendable?

Any other suggestions?

If the payload allows it, they could drop the fairings sooner like they do on Starlink missions. However PPE and HALO most likely cannot be exposed earlier to the high atmosphere so that is likely impossible.

SpaceX may also play with thrust limits a bit, in two ways:
1) Higher nominal thrust (they seem to have done this lately, maybe thrust can be increased even more if the engines only have to be used once
2) Higher G loads near MECO and SECO (less throttling) and tighter max-Q bucket

3) Reduce the delay, and the associated gravity loss, between MECO/second-stage separation and SES-1.

Musk said recently that doing so increases the stress on the first stage, but that doesn't matter for this expendable stage.

Of course, at the higher velocity of Heavy’s second stage separation, compared to that for our regular Falcon 9, that loss would be proportionally less, and so the gain will be small.

[GewoonLukas_]

NASA budget documents now showing this launch for 2025:

Interesting chart in NASA budget documents this morning that show Artemis 3 still launching in 2025, but Artemis 4 pushed back to 2028.

https://twitter.com/jeff_foust/status/1635283787813892100

[gongora]

NASA LAUNCH SERVICES II - SPACEX MOD 260: Add Mission Unique Service for a Mechanical Ground Support Equipment (MGSE) Stand to the Habitation and Logistics Outpost (HALO) + Power and Propulsion Element (PPE) mission.

[spacenuance]

Reading through this thread, I noticed that the generally accepted mass for the PPE/HALO stack was 14-15 tons. However, more recently from Stephen Clark at Ars . . .
https://arstechnica.com/space/2023/10/nasas-falcon-heavy-era-begins-this-week-with-launch-of-asteroid-mission/ [Oct 9]

These two modules, a power and propulsion element and a pressurized habitat for astronauts, are projected to weigh in at about 18 metric tons (nearly 40,000 pounds). That would make this spacecraft the heaviest payload SpaceX has ever launched.

[DanClemmensen]

Reading through this thread, I noticed that the generally accepted mass for the PPE/HALO stack was 14-15 tons. However, more recently from Stephen Clark at Ars . . .
https://arstechnica.com/space/2023/10/nasas-falcon-heavy-era-begins-this-week-with-launch-of-asteroid-mission/ [Oct 9]

These two modules, a power and propulsion element and a pressurized habitat for astronauts, are projected to weigh in at about 18 metric tons (nearly 40,000 pounds). That would make this spacecraft the heaviest payload SpaceX has ever launched.

The article does not mention it, but possibly part of the difference is that PPE will be fully fueled, because it must move itself and HALO from its Earth orbit to NRHO.

[sdsds]

New longer fairing [...]

Was there a status update on the longer fairing, perhaps when the testing at NASA Glenn was completed?

[ZachS09]

PPE/HALO weighing 18 metric tons (~39,683 pounds) is to be SpaceX’s heaviest payload ever?

I thought the heaviest SpaceX payload was 23 Starlink v2 Mini satellites (800 kilograms each), which weigh 18.4 metric tons (~40,565 pounds) all together.

[sdsds]

The article does not mention it, but possibly part of the difference is that PPE will be fully fueled, because it must move itself and HALO from its Earth orbit to NRHO.

Do you mean hydrazine or xenon propellant?

[DanClemmensen]

The article does not mention it, but possibly part of the difference is that PPE will be fully fueled, because it must move itself and HALO from its Earth orbit to NRHO.

Do you mean hydrazine or xenon propellant?

The impression I got was that PPE was going to use its ion thruster  (xenon) to get PPE+HALO out to NRHO, but I do not have a reference for this. I got that impression because I recall that the article said it was going to take months.

[sdsds]

For reference, here's a March, 2020 NASA Technical Memorandum indicating PPE would notionally include:

2.2 Reaction Control System Assumptions
Each RCS thruster is modeled as a hydrazine-fueled 20N thruster with an Isp of 200s

[Elthiryel]

PPE/HALO weighing 18 metric tons (~39,683 pounds) is to be SpaceX’s heaviest payload ever?

I thought the heaviest SpaceX payload was 23 Starlink v2 Mini satellites (800 kilograms each), which weigh 18.4 metric tons (~40,565 pounds) all together.

We don't have a detailed mass of Starlink V2 Mini satellites. We know from the FCC documents that they should weigh around 800 kg, but it may have been published before the design was finalized (especially with SpaceX rapid development) or it could have some margin included.

I actually think the mass may be substantially lower, here's the reasoning. There were a few instances of SpaceX or Elon announcing the heaviest SpaceX payload to date, the last one being Starlink Group 5-2 mission. During the webcast they said that the payload mass is "over 17,400 kg", but also "around 38,000 lb". The logical upper bound seems to be 38,500 lb (otherwise it would be "around 39,000 lb"), which gives us around 17,463 kg. I think if 23 V2 Mini satellites were heavier, they would also announce it, but they did not, so I suspect the actual mass per satellite is below 760 kg.

[gongora]

The article does not mention it, but possibly part of the difference is that PPE will be fully fueled, because it must move itself and HALO from its Earth orbit to NRHO.

Do you mean hydrazine or xenon propellant?

It would need both.