BFS GTO Kickstages (reusable)

[RedKraken]

Several folks have commented on kick stages and tugs for BFS cargo.

Some stuff from reddit and NSF :

https://www.reddit.com/r/SpaceXLounge/comments/7553za/wildass_speculation_thread_20_3b_whoops_i_dun/

https://www.reddit.com/r/spacex/comments/9hys4y/bfr_gto_trajectory_ideas_with_falcon_9like_kick/

https://forum.nasaspaceflight.com/index.php?topic=46412.0

I am interested in reusable methalox kickstage designs that can

• deliver a 7 tonne sat out to GTO (2500m/s),
• then 16 hrs later at perigee burn back into LEO (another 2500m/s sans payload) for a later pickup and return to surface.
• cluster while waiting for pickup in LEO
• can be carried in a carousel on bfs cargo

Why return to surface?

Refuel in orbit might be doable...but payload transfer from BFS to kick would be tricky. Would need an extra berthing system.

Keep it simple.

Just do integration and fueling on the ground and wear the price of lifting 5t extra dry-mass on your 120t lifter.

For example

• 12t of sub-cooled methalox (tanks are ~2m long by 3.0m diameter or another combination with gives ~14 cubic meters of tank space),
• 1 tonne dry mass (~7.7%),
• 10t raptor (100kN, sea-level for simplicity - 356s in vacuum, mass ~50kg)
• Solar / batteries / apu for 16hrs of operation and maybe a few weeks of dormant operation while waiting for pickup.
• Boil-off management up-to 90 minutes for GTO burn fuel(~11t) and  ~16hrs for LEO return fuel(~1.1t), maybe 150hrs for clustering fuel.
• various attitude and ullage thrusters
• payload up to 7t
• Total package ~20t.

 

2018 BFS cargo (120t LEO) could lift a carousel of 5 or 6 of these.

Dump them in LEO, let them GTO burn when they are in position, pickup a cluster of spent kicks from the last mission, and return home for dinner.

Ideas/Comments?

 

Edited September 26, 2018 by RedKraken
gto burn

[Bill Phil]

Burning back into LEO may not be entirely necessary. Could get away with less propellant and use some aerobraking. Not necessarily deep into the atmosphere, but enough to slow it down so that the delta-v to brake is substantially less.

[kerbiloid]

A single-use motor inside. Some tethers, connecting it with the hull at several points. A self-crushing device.
And the spent rocket stage becomes a heavy but compact aluminium briquette waiting in orbit for a future orbital space station with a car-crasher onboard.
Thousands tonnes of aluminium already delivered to the orbit, waiting to be turned into powder for 3d printing..

[RedKraken]

1 hour ago, Bill Phil said:

Burning back into LEO may not be entirely necessary. Could get away with less propellant and use some aerobraking. Not necessarily deep into the atmosphere, but enough to slow it down so that the delta-v to brake is substantially less.

Good point.

I guess it depends how fast you want them back. 

If you want them  for another mission in two weeks time fast-turnaround, you spend the fuel.

If you dont need them for a couple of months, your payload goes up from closer to 8t and do some aero-braking/burn combination.

49 minutes ago, kerbiloid said:

A single-use motor inside. Some tethers, connecting it with the hull at several points. A self-crushing device.
And the spent rocket stage becomes a heavy but compact aluminium briquette waiting in orbit for a future orbital space station with a car-crasher onboard.
Thousands tonnes of aluminium already delivered to the orbit, waiting to be turned into powder for 3d printing..

heh... i would hate to crush my beautiful gto-kicks....

[kerbiloid]

16 minutes ago, RedKraken said:

i would hate to crush my beautiful gto-kicks....

Decouple and save the dense and compact propulsion module, crush the beer can fuel tank.

[magnemoe]

2 hours ago, Bill Phil said:

Burning back into LEO may not be entirely necessary. Could get away with less propellant and use some aerobraking. Not necessarily deep into the atmosphere, but enough to slow it down so that the delta-v to brake is substantially less.

Yes, but it would be an more complex design, purpose here was simply an simple upper stage who did the GTO burn deployed the satelite, it would then lower Pe do an orbit and return to the BFS ship for docking. 
Now the question is how more capacity this 3rd stage would give you, BFR would already have an significant payload capacity to GTO, I assume more than 25 ton. 

For deep space missions this would be interesting, 60 ton 3rd stage think methane centaur stage, then an 20 ton hypergolic for braking and an 10 ton payload for Jupiter or outward. 
Note that this giant kick stage is not very complex, its just huge. 

[RedKraken]

18 minutes ago, magnemoe said:

For deep space missions this would be interesting, 60 ton 3rd stage think methane centaur stage, then an 20 ton hypergolic for braking and an 10 ton payload for Jupiter or outward. 

10 tonne probes to the outer planets is a beautiful thing.... i'd like to order a dozen please.

[Xd the great]

How about a smaller bfs? A bfs in a bfs. Should work. The full scaled one may be suborbital.

[Racescort666]

9 hours ago, RedKraken said:

10 tonne probes to the outer planets is a beautiful thing.... i'd like to order a dozen please.

I mean... NASA has another HST* just laying around...

*ok, not really but the similarities to KH-11 and the donated telescopes are supposedly substantial.

[RedKraken]

6 hours ago, Xd the great said:

How about a smaller bfs? A bfs in a bfs. Should work. The full scaled one may be suborbital.

A small bfs could be exactly what we need considering its dry mass is sitting at about ~75/1200 or 6.25%.

Its a lot more complicated than a kickstage....but it returns to base by itself. No orbital pickups. 

If scaling down works for the drag-o-dynamics of the bellyflop entry....and the drymass.

Not sure about clustering these in a BFS.

it might just be better to do a 1/5 BFR (or SFR)...roughly 880t GLOW and 28t LEO/ 8t GTO.. so GTO class missions don't interfere with moon/mars stuff.

Which is essentially a super-capable Falcon9 replacement operating off falcon9 sized launch pads.

I don't think we will see this anytime soon....but it is interesting to think about.