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

[Jim]

https://www.gao.gov/assets/gao-22-105212.pdf

As of February 2022, the co-manifested vehicle is above the Falcon
Heavy launch vehicle’s mass limit. If the mass is too high, it could affect
the vehicle’s ability to reach the correct lunar orbit. The project is taking
steps to reduce mass, including evaluating whether it needs to
potentially off-load some components for initial launch.

co-manifested vehicle = PPE + HALO

Is there some way SpaceX can up-rate FH to meet the new mass estimate of PPE + HALO?

Cutting weight in design and off loading mass before launch seems like the easiest path forward.

The easiest thing to offload will be fuel, so they have a delicate balancing act to do there. Best of luck to them.

Need all of it to get to NRHO

[sdsds]

Is there some way SpaceX can up-rate FH to meet the new mass estimate of PPE + HALO?

Cutting weight in design and off loading mass before launch seems like the easiest path forward.

Yes. Except the design is complete. Changing the design now would lead to expectation of a significant schedule hit. Off-loading mass sounds good, but that seems to imply off-loading functionality. Integrating that functionality back into HALO once it's in space could be costly.

I'm still hoping someone is going to 'fess up and admit they have mass or performance margin. What happens if the side boosters of FH run their Merlins at above-nominal thrust levels?

[DanClemmensen]

Sorry for an ignorant question: is there a place an outsider can find a quantitative description of this mission? What was the planned mass for PPE/HALO and what was the orbit into which FH was supposed to put it? What is the current estimate of the excess mass?

[GWR64]

https://www.gao.gov/assets/gao-22-105212.pdf

As of February 2022, the co-manifested vehicle is above the Falcon
Heavy launch vehicle’s mass limit. If the mass is too high, it could affect
the vehicle’s ability to reach the correct lunar orbit. The project is taking
steps to reduce mass, including evaluating whether it needs to
potentially off-load some components for initial launch.

co-manifested vehicle = PPE + HALO

The first estimate of launch mass of 14 - 15 t, is close to the value given by NASA for the Falcon Heavy to the moon.
https://elvperf.ksc.nasa.gov/Pages/Query.aspx
With C3 -0.6 km2/sec2  I get a little more than 15 t .
Is that about right for a TLI?

[lrk]

Is the FH currently planned to be fully expended?  If not, moving to a fully expendable launch could be one option.

Another possibility is to lower the target orbit, load additional Xenon for the ion engines and extend the duration of orbit raising.  Might require some re-design to carry additional propellant, though.

One advantage of using electric propulsion is that there can be some flexibility with the orbit insertion.  It should be possible to take advantage of performance reserves by burning the upper stage to depletion, to shorten the orbit raising timeline and save PPE fuel. 

[Jim]

Is the FH currently planned to be fully expended?  If not, moving to a fully expendable launch could be one option.

Another possibility is to lower the target orbit, load additional Xenon for the ion engines and extend the duration of orbit raising.  Might require some re-design to carry additional propellant, though.

One advantage of using electric propulsion is that there can be some flexibility with the orbit insertion.  It should be possible to take advantage of performance reserves by burning the upper stage to depletion, to shorten the orbit raising timeline and save PPE fuel. 

yes

no, can't add more propellant

[Robotbeat]

Is the FH currently planned to be fully expended?  If not, moving to a fully expendable launch could be one option.

Another possibility is to lower the target orbit, load additional Xenon for the ion engines and extend the duration of orbit raising.  Might require some re-design to carry additional propellant, though.

One advantage of using electric propulsion is that there can be some flexibility with the orbit insertion.  It should be possible to take advantage of performance reserves by burning the upper stage to depletion, to shorten the orbit raising timeline and save PPE fuel.

Usually electric propulsion involves nearly continuous thrusting (which means you don’t get nearly as much of the Oberth Effect as high thrust propulsion), but if you’ve already maximized the Isp (often thrusters have an Isp range they can operate in), a thing you can do without adding more propellant is to avoid thrusting at apogee and only thrust near perigee. That gives you the advantage of the Oberth Effect, but at the expense of much more time and potentially exposure to the Van Allen belts (not a problem for human radiation limits as the Gateway stack will be uncrewed at the time, but might be a problem for electronics or the solar arrays).

Electric propulsion gives you a lot of flexibility there if you’re willing to trade time.

[Alexphysics]

Is the FH currently planned to be fully expended?  If not, moving to a fully expendable launch could be one option.

Another possibility is to lower the target orbit, load additional Xenon for the ion engines and extend the duration of orbit raising.  Might require some re-design to carry additional propellant, though.

One advantage of using electric propulsion is that there can be some flexibility with the orbit insertion.  It should be possible to take advantage of performance reserves by burning the upper stage to depletion, to shorten the orbit raising timeline and save PPE fuel. 

yes

no, can't add more propellant

That's actually the first time I hear it is supposed to be fully expended for this mission. As I had understood, the plan was for side boosters to land on droneships and center core to be expended. I was in fact quite upset that they had "mass constraints" given SpaceX could just simply expend the boosters and recover some of that mass constraint.

[whitelancer64]

Is the FH currently planned to be fully expended?  If not, moving to a fully expendable launch could be one option.

Another possibility is to lower the target orbit, load additional Xenon for the ion engines and extend the duration of orbit raising.  Might require some re-design to carry additional propellant, though.

One advantage of using electric propulsion is that there can be some flexibility with the orbit insertion.  It should be possible to take advantage of performance reserves by burning the upper stage to depletion, to shorten the orbit raising timeline and save PPE fuel.

Usually electric propulsion involves nearly continuous thrusting (which means you don’t get nearly as much of the Oberth Effect as high thrust propulsion), but if you’ve already maximized the Isp (often thrusters have an Isp range they can operate in), a thing you can do without adding more propellant is to avoid thrusting at apogee and only thrust near perigee. That gives you the advantage of the Oberth Effect, but at the expense of much more time and potentially exposure to the Van Allen belts (not a problem for human radiation limits as the Gateway stack will be uncrewed at the time, but might be a problem for electronics or the solar arrays).

Electric propulsion gives you a lot of flexibility there if you’re willing to trade time.

The PPE has both electric propulsion, using Xenon, and chemical thrusters, using MMH (monomethyl hydrazine) and MON-3 (mixed oxides of nitrogen).

[sdsds]

With C3 -0.6 km2/sec2  I get a little more than 15 t .
Is that about right for a TLI?

In https://www.ulalaunch.com/docs/default-source/rockets/atlas-v-and-delta-iv-technical-summary.pdf
ULA asserts, "TLI (Trans-lunar Injection) = C3: -2 km 2 /sec 2."

[GWR64]

With C3 -0.6 km2/sec2  I get a little more than 15 t .
Is that about right for a TLI?

In https://www.ulalaunch.com/docs/default-source/rockets/atlas-v-and-delta-iv-technical-summary.pdf
ULA asserts, "TLI (Trans-lunar Injection) = C3: -2 km 2 /sec 2."

Yes, I also found different values, and had to decide.
The NASA website only gives values down to C3: -1.8 km2/sec2 for the Falcon Heavy.
However, the increase in payload mass is only a few 100 kg.

[sdsds]

Yes, I also found different values, and had to decide.

Right! I would assert that the LEO departure shown in the attached graphic puts the spacecraft into cislunar space. Apologies for my units: the radius distances are such that the distance from the center of Earth to the center of the Moon (in a circular orbit) is 1.0.

[sdsds]

Advance apologies for the speculation herein.

In the contract awarded to SpaceX, under what fairing is PPE+HALO slated to fly? Standard size, or the extra big one being developed for another customer?

In either case, is there room inside for additional hardware?

Finally, under what circumstances (if any) would addition of a solid motor, sort of like a stage 3, improve the effective performance of FH?

[DanClemmensen]

Advance apologies for the speculation herein.

In the contract awarded to SpaceX, under what fairing is PPE+HALO slated to fly? Standard size, or the extra big one being developed for another customer?

In either case, is there room inside for additional hardware?

Finally, under what circumstances (if any) would addition of a solid motor, sort of like a stage 3, improve the effective performance of FH?

The PPE (Power and Propulsion Element) IS an additional stage, with two separate types of thruster, and it is designed to be refuelled via connections where it mates to the HALO. In earlier Gateway designs, PPE connected to the ERM, (ESPRIT Refuelling Module) rather than Directly to the HALO. In the current plan ERM will plug into the side of HALO and provide fuel through an interface there and that fuel (both hydrazine and xenon) apparently flow through HALO to PPE.

It's pretty late in the design cycle to either add a stage or make modifications to PPE+HALO and I have no insight into which is harder, but somehow cramming an extra COPV full of xenon into HALO might work. It would be detached and discarded during the first resupply mission to Gateway, so it needs to be sized to go through the docking port.

[sdsds]

somehow cramming an extra COPV full of xenon into HALO might work

That's very creative! And yes, it might work. But see:
https://beyondnerva.com/electric-propulsion/hall-effect-thrusters/

and in particular:

The downside to this type of thruster is that the insulator is eroded during operation [and] the erosion of the propellant channel is the main lifetime limitator of this type of thruster,

So in a slow spiral out to the destination orbit some percentage of the useful life of the thruster is consumed.

[DanClemmensen]

somehow cramming an extra COPV full of xenon into HALO might work

That's very creative! And yes, it might work. But see:
https://beyondnerva.com/electric-propulsion/hall-effect-thrusters/

and in particular:

The downside to this type of thruster is that the insulator is eroded during operation [and] the erosion of the propellant channel is the main lifetime limitator of this type of thruster,

So in a slow spiral out to the destination orbit some percentage of the useful life of the thruster is consumed.

But even before the recent overweight problems, the mission was going to use the PPE for a "slow spiral", taking about nine months to get to NRHO.  The extra thrust for the excess mass is an increment on this, and PPE was originally designed as a space tug.

[Jim]

somehow cramming an extra COPV full of xenon into HALO might work

That's very creative! And yes, it might work. But see:
https://beyondnerva.com/electric-propulsion/hall-effect-thrusters/

Not really.  That would be in the habital portion. Also, no mass allowance for it.   The issue is the initial orbit.

[penguin44]

Forgive me I'm a confused man lol. I've read this thread twice and I still have questions.

What is the actual mass of the payload currently?
Is it a full expendable FH?

[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.

[Jim]

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.  How is it going to attach to PPE? 

They don't have the mass allowance for it.