Is FH really too big for comsats?

[go4mars]

I wonder how low that FH payload would go if they tried to recover the upper stage, too??

2nd stage reuse from GTO will be incredibly expensive to payload mass.  If FHR is 7 tonnes with no upper stage reuse, I believe the thread title can be answered "no", and one could argue it's part of the rationale for the new 10 meter core.  Full reusability that is.

 But this was chatted through years ago during "reusable powered clamshell" discussions.  I don't remember which threads that was spread out on. 

[Dave G]

F9-R 3.5mT GTO

FH-R 7mT GTO

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

Also note: SpaceX has said FH-Booster R should be relatively straightforward,
but FH-R will be much more difficult.

In other words, FH-R will take a lot longer, if it ever happens at all.

[Roy_H]

I wonder how low that FH payload would go if they tried to recover the upper stage, too??

2nd stage reuse from GTO will be incredibly expensive to payload mass.  If FHR is 7 tonnes with no upper stage reuse, I believe the thread title can be answered "no", and one could argue it's part of the rationale for the new 10 meter core.  Full reusability that is.

 But this was chatted through years ago during "reusable powered clamshell" discussions.  I don't remember which threads that was spread out on.

I disagree with your statement about expense of recovery of upper stage. Yes it will be very difficult because of the requirement for thermal shielding etc, but not high in fuel costs. Payload hit will be minimal. The upper stage will remain in orbit (most likely 1 full day) until it is in the right position to return to launch site when re-entering earth atmosphere. It does not have to have a long boost back trajectory like the first stage.

[Coastal Ron]

F9-R 3.5mT GTO

FH-R 7mT GTO

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

Also note: SpaceX has said FH-Booster R should be relatively straightforward,
but FH-R will be much more difficult.

In other words, FH-R will take a lot longer, if it ever happens at all.

Haven't heard any mention of cross-feed recently, but that was supposed to be required for the 53mt version.  Since the cross-feed system would likely add more complexity and weight, I wonder how that would affect reusability?  And where does that come into play with the capacities to GTO?

For instance, I would imagine that the FH-Expendable could be cross-fed, but FH-R would not (or maybe even "could not")?

Lot's of combinations of factors at play here.  But if there are lots of combinations of capabilities, then that would mean that Falcon Heavy could cover the entire range of comsat needs, and still be less expensive than competitors like Ariane 5 and Atlas/Delta.

Or SpaceX may self-limit their configurations to cut down on managing too many variations.

[guckyfan]

Also note: SpaceX has said FH-Booster R should be relatively straightforward,
but FH-R will be much more difficult.

I don't think it is more difficult. It just takes a huge amount of fuel so causes a big payload hit. But if you have a comsat within that weight range you can still do it.

[Roy_H]

Haven't heard any mention of cross-feed recently, but that was supposed to be required for the 53mt version.  Since the cross-feed system would likely add more complexity and weight, I wonder how that would affect reusability?  And where does that come into play with the capacities to GTO?

For instance, I would imagine that the FH-Expendable could be cross-fed, but FH-R would not (or maybe even "could not")?

Cross-feed and re-useability are separate issues and not dependent on each other. The 53mT capacity is ultimate, that is using both cross-feed and expendable. No reason why a cross-feed core stage cannot be landed, and I think it is only practical from the Brownsville, Texas launch site where the center core would land in the Florida Keys.

[Dave G]

Cross-feed and re-useability are separate issues and not dependent on each other. The 53mT capacity is ultimate, that is using both cross-feed and expendable.

53mT is for low earth orbit, and not relevant for comsats, so its off-topic for this thread.

For the previous numbers:

FH-R 7mT GTO

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

I believe these are all cross-fed.  For a cross-fed FH, returning the center core back to the pad (fully and rapidly reusable) is hard.   The center core is almost like a second stage.

[LouScheffer]

Cross-feed and re-useability are separate issues and not dependent on each other. The 53mT capacity is ultimate, that is using both cross-feed and expendable.

53mT is for low earth orbit, and not relevant for comsats, so its off-topic for this thread.

For the previous numbers:

FH-R 7mT GTO

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

I believe these are all cross-fed.  For a cross-fed FH, returning the center core back to the pad (fully and rapidly reusable) is hard.   The center core is almost like a second stage.

My calculations indicate they don't need crossfeed, or even center throttling, to get 7mt to GTO.  Just burn all three in parallel, so recovering the middle booster is no harder than the others (though they are all harder than the F9, since they burn out further downrange and going faster than the single core case).

Throttling down the center core until booster sep (as Delta-IV does) and ultimately cross-feed, will increase payload but make the center booster harder to recover, as many have pointed out.  I suspect only SpaceX can figure accurate numbers for these cases, and even then only after they recover a few stages and have a good idea of the fuel needed.

[sdsds]

Analagous to the Grasshopper prototype technology development vehicle that was built on an old F9 v1.0 first stage, Skyhopper could be a limited run set of FH second stages with some technology additions to assist SpaceX in testing out some of their reusable second stage design ideas

Yes. In particular the propellant needed for non-destructive re-entry propulsion could consume much of the "excess" mass budget.

Consider the case of payload delivery to an 80000x295 km transfer orbit. A destructive re-entry from there could be accomplished with a 14 m/s retrograde burn at apogee. That puts the perigee at 50 km, where the velocity would be 10,743 m/s. In contrast consider a two-burn re-entry profile, first reducing the apogee to a 2000x295 km orbit and then reducing perigee to 50 km. For that approach the velocity at the 50 km perigee would be a somewhat more survivable 8,377 m/s, but the delta-v to perform the maneuvers is something like 2,440 m/s.

Translating that 2,440 m/s of delta-v into propellant mass would require making assumptions about the dry mass of the stage. But it's fairly clear that maneuvers of that size would require lots of propellant!

(WARNING: My orbital mechanics spreadsheet could be wrong!)

[Dave G]

My calculations indicate they don't need crossfeed, or even center throttling, to get 7mt to GTO.

OK, so that leaves:

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

that use cross-feed.

In other words, with cross-feed, the center core is always expendable.

[Lars_J]

http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog:04ce340e-4b63-4d23-9695-d49ab661f385&plckPostId=Blog:04ce340e-4b63-4d23-9695-d49ab661f385Post:41fcfd6c-a6f2-42d5-b20b-52e31a103011


F9-R 3.5mT GTO

FH-R 7mT GTO

FH-Booster R 14mT GTO

FH-Expendable 21mT GTO

Does anyone know how these options translate to LEO payload capacity?

[Dave G]

Does anyone know how these options translate to LEO payload capacity?

Off topic for this thread.  For LEO, F9 is more than adequate for any comsat.

[MP99]

I wonder how low that FH payload would go if they tried to recover the upper stage, too??

2nd stage reuse from GTO will be incredibly expensive to payload mass.  If FHR is 7 tonnes with no upper stage reuse, I believe the thread title can be answered "no"...

Agreed.

Cheers, Martin

[Lobo]

Also note: SpaceX has said FH-Booster R should be relatively straightforward,
but FH-R will be much more difficult.

I don't think it is more difficult. It just takes a huge amount of fuel so causes a big payload hit. But if you have a comsat within that weight range you can still do it.

This is why I think (my speculation) that one of the "markets" for a SpaceX fully reusable, HLV with 10m core, is these heavier payloads to GTO, GSO and escape.  (Or two payloads like Ariane 5)   It will have a lot of margin so that big reusable upper stage can get to those orbits, deploy the payload, and then do the burns necessary to get back to Earth and land propulsively.  A bit like how STS was a HLV to take EELV-heavy payloads to LEO.  A HLV that could take EELV-heavy payloads BLEO (being more powerful and lighter than the Shuttle, obviously)
If it can be processed and reflown affordably, then that and your fuel are your major launch costs, not the hardware itself. It could replace FH for those types of payloads, while acting as a test bed and money generator for their eventual MCT and Mars abitions.

[CuddlyRocket]

If [a SpaceX fully reusable, HLV] can be processed and reflown affordably, then that and your fuel are your major launch costs, not the hardware itself. It could replace FH for those types of payloads, while acting as a test bed and money generator for their eventual MCT and Mars ambitions.

The cost of construction still has to be amortised over the expected number of flights and I'd expect that to exceed at least the fuel costs. But I think the construction costs may well be less than those of an FH, so I think there's a good chance it will replace the FH for all types of payloads.

[Burninate]

There is an intermediate option where 2 cores are recovered at significant payload cost in proximity to the launch site, and the third burns up in a hypersonic reentry.  This might allow for launching (as a blind guess) maybe a 13 ton (EELV class) payload to GTO, at a very similar cost to a Falcon 9 launch.

The complexity of hypersonic reentry, and of the organizational & liability overhead of recovering something a thousand kilometers downrange, is likely to push the third-core reusability back a ways.

edit: If the boosters separated while still in the lower atmosphere, *very* early, effectively generating two vertical Grasshopper tests plus a normal F9 launch from 10km height, would that account for the payload cost structure seen now, without multiple payload piggybacking?

[Adaptation]

This is how I understand the situation, sorry if its a little basic. 

So comsats like GEO so ground stations don't have to track.  From an RF point of view you want separation between you and anyone else using a similar frequency.  With a few degrees of separation and decent gain antennas (directional) you can reuse all the same frequencies as another satellite without any interference issues.  But GEO lies on the equator and there are only a few slots over a range of latitudes with enough separation. 

And now the question.

How much 'station keeping' would it require to maintain an artificial 'stationary' orbit that would naturally be inclined 4° but is purposely kept 4° north +-0.5°.  Would a large solar array and electric thrusters be feasible to maintain this position? 

Alternatively (and even more futuristically) could a long tether with a counterweight be used to keep a satellite in such a position.

[douglas100]

The plane of the orbit you describe does not pass through the centre of the Earth. Continuous thrusting is needed to maintain such an orbit.

Your question really belongs in Advanced Topics.

[Proponent]

How much 'station keeping' would it require to maintain an artificial 'stationary' orbit that would naturally be inclined 4° but is purposely kept 4° north +-0.5°.  Would a large solar array and electric thrusters be feasible to maintain this position?

Absolutely not.  The acceleration of gravity at GEO is about 0.3 m/s².  Since 4^o is equivalent to 0.07 rad, the required acceleration would be about (0.07)(0.3 m/s²) = 0.02 m/s².  That doesn't sound like much, but over a day (86,400 s), it's a delta-V of 1800 m/s.

An appropriately-angled solar sail might offer some hope, but it's going to be a little complicated, especially if occasional passages through the earth's shadow need be factored in.  I think Robert Forward or Colin McInnes may have written something about this.
 

Alternatively (and even more futuristically) could a long tether with a counterweight be used to keep a satellite in such a position.

That would be an interesting dynamics problem.  The tether will be a few thousand kilometers long and will itself present a substantial cross-section and possible collision hazard.

EDIT: "dynamics problems" -> "dynamics problem";
           "1800 km/s" -> "1800 m/s", per MP99 (thanks!)

[LouScheffer]

This is how I understand the situation, sorry if its a little basic. 

How much 'station keeping' would it require to maintain an artificial 'stationary' orbit that would naturally be inclined 4° but is purposely kept 4° north +-0.5°.  Would a large solar array and electric thrusters be feasible to maintain this position? 

Alternatively (and even more futuristically) could a long tether with a counterweight be used to keep a satellite in such a position.

It would take far too much fuel to 'hold' a satellite there, even with electric propulsion.  And a tether does not help, since the forces are towards the equator and would put the tether in compression, not tension. 

However, a satellite in such a position will naturally oscillate back and forth from north to south.  If instead of one satellite in the slot, you put (for example) 8, and space them out and let them all oscillate, then there would always be one north of the equator, one near the equator, and one south of the equator, though which one is in which position will switch.  This might be a sensible way to trade off satellite cost for increased capability.