Reusable GTO architecture

[LouScheffer]

As many people have pointed out, LEO reusability can work even if the mass penalty is fairly big.  For example, if the needed recovery hardware masses 4 tonnes, almost as much as the existing stage, you would still get a reasonable payload of 18-19 tonnes to LEO.

However, such a penalty would reduce the GTO payload to an almost useless amount.  Furthermore, the penalty mass would likely be even larger since the GTO entry would be more energetic.   So re-usable GTO looks unlikely with the current architecture.

But if you really need completely re-usable GTO, here's one possible approach.  You divide the task into two parts, getting to LEO and LEO-GTO.  The Earth to LEO piece is whatever SpaceX comes up with for this task, for which there is much speculation already. The LEO-GTO part is handled by a re-usable transfer stage, which does LEO->GTO like usual, then aerobrakes back into LEO for the next cargo.   Since you can do aerobraking with no heatshield, the mass penalty is much less (as Mars missions have shown).

The numbers look plausible.  You could build the tug like the current second stage with smaller tanks.  You need only about 10 tonnes of fuel, so the tanks are 1/10 the size of the current second stage.   Mass largely scales as tanks + engine, so maybe 2000 kg to start.  Now you need the hardware to keep it alive, and do the maneuvering for aero-braking.  The delta-V requirements are small - to drop the perigee to 100 km from a 200x36000 km orbit, you need only about 10 m/s.   After braking, you need to raise the perigee.  Going from 100x200 to 200x200 takes another 30 m/s.   Add in the maneuvering to keep the braking under control, and perhaps you need 100 m/s.  That's about 120 kg of hydrazine used in mono-propellant thrusters.  Then you need solar panels and batteries to keep the stage alive, radios to control from the ground, and perhaps a better INS with Sun or Earth sensors.   500 kg should be enough for a total stage mass of 2500 kg.

So now the LEO flights comes up, transfers 10 tonnes of fuel, 6 tonnes of satellite, and 100 kg of hydrazine, then returns to Earth.  The tug fires into GTO, releases the satellite, then aerobrakes back down, ready for the next payload.   With 10 tonnes of fuel, and a final mass of 8.5 tonnes, the tug can do 348*9.8*ln(18.5/8.5) or 2650 m/s, enough for a somewhat super-sync  (GEO-1700 or so) transfer orbit.  The main drawback is that without a heat shield aerobraking can take months, so you'd need several of these tugs if you wanted a fast launch cadence. 

So what would need to be developed?  Automated rendezvous already exists, as does transfer of hydrazine.  Aerobraking has been done at Mars and Venus, and presumably Earth would be easier.  So you need to develop transfer of cryogenic fuel and a payload.  Long term cryogenic storage is not needed - the fuel is used within one orbit of transfer.

[livingjw]

Why not add a heat shield?
 John

[Robotbeat]

Betcha ITSy has plenty of performance to fly to GTO with full reuse in a single shot. With a large bird. Supersynch, even.

[yokem55]

Betcha ITSy has plenty of performance to fly to GTO with full reuse in a single shot. With a large bird. Supersynch, even.

And if it flies often enough may even be cheaper to fly than Falcon 9 or Heavy.

A tug is a great idea, but it adds a lot of mission complexity when brute force can be both cheaper and simpler.

[John Alan]

I like the idea... tugs in orbit...

I will put a related idea of mine out there...
SpaceX will price delivery to LEO with recovery of S2 such that satellite makers see the light and built much larger tanks and thrusters into their birds... Self service Tugs in other words...   
ITSy is a prime example of such a delivery vehicle to haul several of these 'hybrids' into orbit per flight...

Point is... at some point the launch providers and the bird builders have gotta work together to divide the workload to GEO in a manner that actually puts working parts on station at the lowest cost... And gets reusable parts back on the ground to be flown again...

Just my two cents... 

[hkultala]

As many people have pointed out, LEO reusability can work even if the mass penalty is fairly big.  For example, if the needed recovery hardware masses 4 tonnes, almost as much as the existing stage, you would still get a reasonable payload of 18-19 tonnes to LEO.

However, such a penalty would reduce the GTO payload to an almost useless amount.  Furthermore, the penalty mass would likely be even larger since the GTO entry would be more energetic.   So re-usable GTO looks unlikely with the current architecture.

Since you can do aerobraking with no heatshield, the mass penalty is much less (as Mars missions have shown).

Here you have two contradictionary statements.

If you can do aerobraking from GTO to LEO with no heatshield, you do not need bigger heatshield or more recovery hardware for the normal reusable GTO second stage. You can then just use the LEO-optimized heat shield for actual re-entry, and first just aerobrake it from GTO to LEO before doing the actual re-entry.

[LouScheffer]

As many people have pointed out, LEO reusability can work even if the mass penalty is fairly big.  For example, if the needed recovery hardware masses 4 tonnes, almost as much as the existing stage, you would still get a reasonable payload of 18-19 tonnes to LEO.

However, such a penalty would reduce the GTO payload to an almost useless amount.  Furthermore, the penalty mass would likely be even larger since the GTO entry would be more energetic.   So re-usable GTO looks unlikely with the current architecture.

Since you can do aerobraking with no heatshield, the mass penalty is much less (as Mars missions have shown).

Here you have two contradictionary statements.

If you can do aerobraking from GTO to LEO with no heatshield, you do not need bigger heatshield or more recovery hardware for the normal reusable GTO second stage. You can then just use the LEO-optimized heat shield for actual re-entry, and first just aerobrake it from GTO to LEO before doing the actual re-entry.

True.  In fact you can aerobrake it very quickly, just one or a few passes, if it has a heat shield.  The main problem is hauling the heat shield, leg mass, and other auxiliary items to GTO orbit.  You may still need some extra hardware for orientation in GTO orbit, control from Earth to compensate for atmosphere variations, and longer life on orbit.

[BeamRider]

Can someone outline the present F9 / Atlas V GTO profile(s), WRT the trajectory and disposition of the second stage after payload sep, including any post-sep delta v maneuvers? That would set a baseline for the current state of practice.

[TrevorMonty]

This OTV is future ULA see for ACES.

[LouScheffer]

Can someone outline the present F9 / Atlas V GTO profile(s), WRT the trajectory and disposition of the second stage after payload sep, including any post-sep delta v maneuvers? That would set a baseline for the current state of practice.

There are three profiles in common(ish) use:

By far the most common is the leave the final stage in a roughly 300 km x GEO orbit. with no explicit de-orbit..  It then decays by itself in less than 25 years, the commonly used standard.

Probably next common, for lighter missions, is to leave the stage in a 4000 km x GEO orbit.  No explicit de-orbit, and it will be up there for millennia, but not a big problem.

I think perigees between these two are forbidden, by convention if not by treaty, since they hang around for a long time and cross heavily traveled orbits.

The final, least common, disposal is to haul the satellite all the way to GEO, then bump the stage into a nearby disposal orbit (also used by end-of-life comsats).  Here a disposal burn is mandatory to get the booster out of GEO, but it's very small.  This profile is only used by military sats, to my knowledge.

[GWH]

In regards to a reusable GTO tug and ITSy I don't see any reason why the two would be mutually exclusive.

With the significant capacity to LEO of the ITSy, carrying propellant as a secondary payload to store in a depot or in orbit ITSy ship would make a lot of sense.  This would be especially true if SpaceX is trying to fund their own way to Mars.

Yes a dedicated tanker would be simpler on a mission to mission basis - but each flight is going to have its costs for operation and refurbishment of hardware that may be very expensive starting out. 

[john smith 19]

Point is... at some point the launch providers and the bird builders have gotta work together to divide the workload to GEO in a manner that actually puts working parts on station at the lowest cost... And gets reusable parts back on the ground to be flown again...

Not really. A tug can do a transfer orbit provided it's a "resonance orbit" IE it does 1 orbit (up down) to N orbits of the US, provided the payload can manage the final circularization burn.

If the sat has a liquid propulsion system that first drives the AKM engine, the switches to orbit keeping thrusters this is not a major challenge. Trickier with ion thrusters but while builders say you can have them I'm not really sure how many operators have actually gone that way, given it turns a single pass through the Van Allan belt into a a month long multiple spiral slow roast. Some will think it worth it, some won't. 

The real major challenge remains what it's always been for SX, making the 2nd stage reusable.

We've seen them say they can, then they won't, now they might try on the FH debut flight. Given Musk's stated views on reuse I don't think they've given up, but I do think they've discovered it's even more "super damm tough" than they thought. 

While the US remains expendable there cannot be any really radical reductions in $/lb to orbit. Saying MCT/ITS/ITSy/ITS-Lite/Whatever will do it simply ducks the question.

Betcha ITSy has plenty of performance to fly to GTO with full reuse in a single shot. With a large bird. Supersynch, even.

And ITS would have even more excess performance.

However how many comm sat operators can wait another decade before they put their payload up while it's being developed?

[Robotbeat]

Who says you'd have to wait a decade?

[john smith 19]

Who says you'd have to wait a decade?

I'll answer that in 2024.

[Lar]

Who says you'd have to wait a decade?

I'll answer that in 2024.

Sounds like a bet in the making?

[TrevorMonty]

LEO-GEO OTV makes more sense as that is target destination for payloads. With GEO OTV GEO satellites can be smaller, lighter and cheaper as they don't need GTO-GEO DV and propulsion systems.

A GEO tug can also be used for delivering payloads to Lunar  orbits eg DSG at NRO

[john smith 19]

Sounds like a bet in the making?

Not really, as I win either way.

If SX do manage to exceed my expectations they have a better chance of getting to Mars faster, which is good.

If they don't my ability to call the schedule is vindicated.

Musk was asked (in 2014) how long the next generation after F9 would take and he said "Optimistically" 5-6 years, which I took as 8-10 years (other posters normally double Musks estimates).

But at that point FH was only a year behind it's first expected flight date and the ITS composite tank had not failed. 

It's now Q317 and still no FH launch (is late Q417 still possible, or is it now definitely NET 2018?)
That's relevant because FH was meant to be the easy upgrade to the F9 architecture (even with propellant cross feed).
I know, "learning curve" improvements in structure and engines make cross-feed unnecessary. But it seems launch noise turns out to be a very much more serious issue when you have 27 of them going flat out than 9.

Then the big LOX tank did burst (I wonder if XCOR's "Unburnium" IP is still available?) and Musk is saying ITS will be re-scoped, details at next IAS meeting.

Now it could be that SX have learned so much getting FH to first flight that that's managed to cut years off the ITS development, except if that were the case, wouldn't they be sticking with the full size one?

That's before we recall that ITS is not 100 tonnes to LEO (IE 4x F9 or < 2x FH) it's 100 tonnes to Mars, with a new engine, new fuel, new tank material, new range (24 000 miles, or roughly 1/10 of the way to the Moon, up to 140 000 000 miles)

My view is as the number of new things increases the risk multiplies, and everything about ITS is new.

In fact having read over what I've just written I think 2024 may be quite ambitious. 
But we're going to find out one way or another.