Falcon Heavy Distributed Lift Concept(s)

[RyanC]

Was going to post this in the SLS v FH thread, but it got locked before I could post :-(

Per Elon on Twitter, the cost of FH in expendable mode is $150 million.

A 60 tonne departure stage with a pmf of 0.925 would be:

55,500 kg propellants (52,447.5 kg useable if we assume 0.945 propellant utilization)
3,052.5 kg trapped propellant
4,500 kg stage mass/engine/etc.

Cranking some numbers using Merlin 1D Vac, 348 ISP for the departure stage

[using equation: C3 = (ΔV + 7.8)^2 - 11^2 ]

80 km2/s2 C3 capability (Jupiter Direct, 2~ years) = 2,000~ kg
20~ km2/s2 C3 capability (VEEGA, 6.6+ years) = 15,000~ kg

If SpX went crazy and decided to put Raptor onto that departure stage with 375 ISP, the numbers shake out to:

80 km2/s2 C3 capability (Jupiter Direct, 2~ years) = 3,700~ kg
20~ km2/s2 C3 capability (VEEGA, 6.6+ years) = 18,340~ kg

Europa Clipper weighs about 9,200 kg for the entire stack (Clipper + Lander, Braking/Descent Stages, etc).

Even SLS can't send the full up Europa Clipper direct (it can only send 5,200 kg directly and 13,300 kg via VEEGA); which makes Europa Clipper workable with a Merlin 1D departure stage.

Essentially, a two launch campaign for SpaceX could send SLS' flagship mission to Jupiter via:

Falcon Heavy Expendable ($150M) to place into orbit 60T departure stage (DS).

Falcon Heavy Reusable ($90M) to place into orbit 9.2T Europa Clipper + Several Tonne Manouver Stage which would manouver the EC+MS stack to an autonomous docking with the DS.

Following docking, after perfunctory checks, the departure stage can fire it's engine(s) for departure from earth orbit.

Naturally, the above is greatly simplified; as you'd need to account for boil-off in the Departure Stage over a period of perhaps 24-48 hours before docking+departure from LEO; but this is lessened by SpX's choice of propellants for Merlin, and it could be ameloriated by a small regenerative cooler for the Departure Stage's LOX tank.

But major bulletpoints of the above approach are:

A.) Cost: $240M vs $500M to $1B< for launch costs.

B.) No need to develop complex cryogenic fuel transfer; as the Departure Stage (DS) would be self contained.

C.) Leverages technologies already at pretty decent TRLs, such as autonomous docking, long duration coast stages, and some anti-boil off techniques.

Best part is, the design of the Merlin powered Departure Stage would not have to be very complicated, it can be a shortened version of the Falcon 9 Upper stage:

Falcon 9 Block 1 Stage 2: 52~ tonnes
Falcon 9 v1.1 Stage 2: 99~ tonnes
Falcon 9 v1.2 FT S2: 116~ tonnes

The biggest stumbling block I see is time.

Specifically, launch campaign times.

SpX needs to demonstrate that it can launch off missions at/on schedule under time constraints -- because from off the top of my head, you'd want to launch the Departure Stage first, and make sure it's working on orbit, before you begin the launch for Europa Clipper, but Europa Clipper's launch can't have a significant time delta over the Departure Stage's launch(a day or two at least) due to boiloff issues, etc.

NOTE: SLS curves in this are extracted via a graph digitization program from the other curve attached to this post.

NOTE II : yes, I know the pmf of 0.925 and propellant utilization factor of 0.945 for the Departure Stage are heavily sandbagged.

NOTE III: The shaded red area on the C3 Curve is Mars Worst Case and Mars Best Case for C3 (Dependent on what time of the synodic cycle you go to mars at). The Line at 80 km2/sec2 is the C3 burn directly to Jupiter system.

[RyanC]

There's also the alternative to a 60T Departure Stage as cargo -- someone else proposed it in this forum -- you basically lengthen S2 and make S2 the payload itself; so that you have a half-full S2 in orbit with a significant amount of propellant for a departure burn. Might be cheaper and more realistic to design than figuring out a way to anchor a 60T load to the FH stack during launch.

[speedevil]

There's also the alternative to a 60T Departure Stage as cargo -- someone else proposed it in this forum -- you basically lengthen S2 and make S2 the payload itself; so that you have a half-full S2 in orbit with a significant amount of propellant for a departure burn. Might be cheaper and more realistic to design than figuring out a way to anchor a 60T load to the FH stack during launch.

Indeed - if you're sticking another merlin vac on the payload, and a payload adaptor, and ... - for S2 to come out worse, it needs to get a lot heavier - and unless the tanks need reinforced beyond their current level a lot - that's going to be hard.

As an aside, stretched S2 can almost be run off falcon heavy reusable, get a few tons to LEO, do a truly prodigious retroburn, and come in at energies comparable to S1, ending up with a final weight and size very comparable to the fairing which they will have recovery expertise on by then.

[TrevorMonty]

Lower cost option is f9 launched payload with small service module for docking to FH US, this service module would allow for loitering for few weeks. The FH would launch second with just small service module give docking propulsion attach to US, half full(50-60t) US would dock with payload with few hours of launch then do departure burn.

[Flying Beaver]

Small issue of two FH launches within 24-48hrs, having only 1 heavy capable pad on the east coast.

[rst]

Small issue of two FH launches within 24-48hrs, having only 1 heavy capable pad on the east coast.

It's likely that by the time SLS EM-2 launches, there'll be another one at Boca Chica.

[acsawdey]

Using the numbers from here https://forum.nasaspaceflight.com/index.php?topic=45033.msg1790687#msg1790687

Step 1: Launch EC with docking adapter into LEO. This can be done with F9 RTLS or ASDS. EC already uses storable propellant so it can wait on orbit for a while.

Step 2: Launch FH with just a docking adapter on S2 (500 kg?). Expending only center core still gets you 87 tons fuel. And F9/FH S2 dry mass is though to be around 4.5 tons anyway so just use it as a departure stage. FH S2 docks with EC. Exit, stage left.

delta-v = 6.8 km/s
Using your equation c3 = (6.8+7.8)^2-11^2 = 92

That seems rather high. Where did I go wrong?

The advantage of doing it this way is that you don't have to depend on a fast turnaround of the pad. EC is meant to cruise for many years anyways so having to wait a couple weeks for its departure stage to arrive isn't a big addition. And the S2 mission as a departure stage just requires an instantaneous launch window and rendezvous with no extended duration.

The part that requires development is the rendezvous and docking.

[Brovane]

Small issue of two FH launches within 24-48hrs, having only 1 heavy capable pad on the east coast.

If there was actually demand for dual FH launches, I am sure that SpaceX could modify LC40 to also support FH launches. 

[RyanC]

That seems rather high. Where did I go wrong?

I think you didn't "sandbag enough".

http://www.spacelaunchreport.com/falcon9ft.html

Gives an estimate of F9 v1.2 FT Upper stage masses as:

4.5 tonne burnout mass.
116 tonne gross mass.

Assume that only only 80T of propellant is actually available on orbit (various reasons, boil off; manouvering, etc etc).

4.5T Falcon 9 Upper Stage Mass (dry).
75.6T of useable propellant from an utilization factor of 0.945
4.1T of trapped/reserve propellant not used for calculations
0.53T International Docking Adapter
---------------------------
9.2T Europa Clipper
1.5T Manouver Stage for Europa Clipper (mass at docking, weighed more but used up fuel to manouver to dock)

Total Stack Mass: 95.43T
Stack Mass at Burnout: 19.83T
ISP of Merlin 1D Vac: 348
Delta V = 5,364 m/sec
C3 = 52.3 km2/s2

If we lightened up the sandbagging a bit more; so that 84T of propellant was available on orbit and that the utilization factor was 0.965, it would become:

4.5T Falcon 9 Upper Stage Mass (dry).
81.06T of useable propellant from an utilization factor of 0.965
2.94T of trapped/reserve propellant not used for calculations
0.53T International Docking Adapter
---------------------------
9.2T Europa Clipper
1.5T Manouver Stage for Europa Clipper (mass at docking, weighed more but used up fuel to manouver to dock)

Total Stack Mass: 99.73T
Stack Mass at Burnout: 18.67T
ISP of Merlin 1D Vac: 348
Delta V = 5,720 m/sec
C3 =  61.8 km2/s2

[RyanC]

Another thing to consider is that distributed lift is now economically feasible thanks to FH.

SLS costs about $1B a launch for 70~ T ($14,285/kg)

A notational Delta IV Super Heavy with 7 CBCs lifting 60T (https://forum.nasaspaceflight.com/index.php?topic=24640.80) if you assume a cost of $100M per CBC, would cost about $700M to launch ($11,666/kg)

Cheaper than SLS, but not enough to overcome the issues of on-orbit docking etc, which would need additional $$$ to overcome.

But along comes FH with it's $2,500/kg cost to orbit, for a fully expendable version. Suddenly, the financial case for distributed lift is now "closing", so to speak.