Starship On-orbit refueling - Options and Discussion

[TheRadicalModerate]

We shouldn't be too hysterical about the Van Allen belts. Apollo 14 (which came through near the thickest parts of both VA belts, both out and back) gave the crew a total dose of about 10 milligreys. (A CT scan is about 8mgr.)

The particles also aren't overly penetrating, compared to cosmic radiation, and secondary (shotgun) radiation from the skin isn't an issue. So combining the skin of Starship with a radiation shelter made from your water storage should protect the passengers for a good month of exposure, if they wanted to.

The VA belts are extremely dangerous for an unprotected human. But an "unprotected human" in space died before the airlock finished depressurising.

There's a lot of difference between a TLI trajectory, which transits both the inner and outer belts at something fairly close to maximum velocity, and, say, an LEO+2500 HEEO, which has a period of 11.5 hours and would likely spend a third of that deep in the outer belt.  I haven't done the time-of-flight computations, but my guess is that we're talking about several times the length of exposure that you get on a straight TLI burn.

Beyond that, what are the contingencies for a difficult rendezvous and docking?  You have close to 10 hours to achieve the R&D and transfer prop.  That should be plenty of time, but what if something goes wrong?  Do you abort the mission if you can't do a one-pass refueling?  Or do you expose the crew to still a third pair of passes through the VA belts?

Using either a TLI-based R&D for refueling or the pusher/tanker eliminates all of that risk, and incurs very little additional risk of a failed refueling, because both the tanker and the payload SS can always do a free-return around the Moon if they can't hook up.  Beyond that, the P/T guarantees a single R&D operation in LEO, where it's easiest to come fetch the crew if something goes wrong.

For cargo missions, none of this likely matters.  For crewed missions, it's a different story.

[TheRadicalModerate]

However, for the Moon or Mars, there's virtually no inclination requirement (Figures below). Hell, you can boost from polar orbit if you want, with barely a hit. So any LEO depot works for BEO missions. LEO-to-GEO is more restrictive, but low-inclination-LEO to equatorial-GEO hides most sins. So a general LEO depot for equatorial boost is likely to see a reasonable amount of use, IMO.

Two reasons you might want a high-inclination departure for the Moon:

1) It can minimize LLO insertion delta-v for lunar polar missions, which a likely to dominate the manifest.

2) High-inclination insertions avoid the thickest part of the VA belts, reducing radiation exposure.

[xvel]

If 250t thrust raptor will exists, SH will be able to raise the tanker with 2100t of fuel, which should provide 160t of fuel on LEO instead of 100t, from my calculations even bigger tankers works very well and are superior to multiple launches of smaller tankers. If SH has 250t engines, delta V is smaller and final angle is more vertical which makes landing easier, "only" problem is that this big tanker due to its weight and more vertical start has bigger gravitational losses so it should probably have more engines

I assume a dry weight of 120t, I don't think the tanker will be lighter, and I'm even afraid it may be heavier because it requires more 4mm rings.

(hkultala was right, you don't need a bigger booster if you equip SH with 250t engines)

[TheRadicalModerate]

You use one of the tankers as a pseudo-depot, you launch the mission ship itself last. If weather delays a fuel launch (or it fails), your crew are still on the ground. You only launch once the tanker-cum-depot has enough fuel for the mission. Then the tanker-depot lands and goes back into ordinary service.

I've been calling this the "aggregation tanker".  It's no different from the vanilla-flavored tankers (unless you drink the Pusher/Tanker Kool-Aid); it's just the one that receives the prop from the other tankers to minimize the number of rendezvous/dock/refuel operations that have to be performed against the live payload.  You potentially need two aggregation tankers, one for LEO top-off and one for either HEEO or post-TLI top-off.  (Of course, if you use P/T, it is the agg tanker, and you only need one, and one rendezvous/dock/refuel.)

[Aside: The same reasoning says that the first "passenger" Starships would just be cargo ships with a passenger pods. Different pods for different missions. Lets you do Shuttle-like missions with mixed cargo and personnel. Such as satellite recovery missions, service missions, mixed science missions, etc. And the latter lets researchers use Starships as single-purpose specialised space-stations, by swapping out mission pods.]

And this because of its likely shape, needs to be called "StarKist".

I think this is no-brainer absolutely the way to engineer a Starship-based crew system, but it's surprisingly controversial.

[hkultala]

[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

[Keldor]

[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

You could potentially use a high inclination orbit and avoid the Van Allen belts almost completely.  This should only cost DV during the initial launch to orbit, before refueling, since once you're in orbit, the rotation of the Earth doesn't effect you.  You'd have a slight loss of efficiency landing on the Moon, but it's rotation speed is so slow that it won't make much difference.

[kkattula]

Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

[TheRadicalModerate]

[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times, not a big deal.

I'm too lazy to do the math here, so correct me if I'm wrong:  You do better refueling at the highest energy possible, as long as you use the energy optimally.  For any EO, that means burning at the next perigee.  But TLI is the highest energy you'll need to get to the cis-lunar orbits, and it doesn't even need to do a second burn to complete the maneuver.  So refueling after TLI should be somewhat more efficient than refueling at HEEO.  (Technically, TLI is an HEEO...)

20 hours is likely enough time to do the rendezvous, dock, prop transfer, and undock.  But any glitch in the system leaves the crew in a dicey situation.  For example, if you had some problem that prevented you from doing the perigee burn with the main engines, you probably need to abort by chopping the perigee enough to reenter, using thrusters (it's not much delta-v).  Doing an indefinite number of passes through VAB would be bad.

You're in no worse shape refueling in TLI, and arguably in better shape because a free return will bring you back to reentry.

Of course, none of this is an issue with the pusher/tanker, since the P/T does one rendezvous in LEO and stages off, leaving the SS with enough prop to do the rest of TLI and everything needed to land and get home.  It's absolutely not as efficient as a tanker rendezvous in TLI, but it's fewer docking operations.

[Twark_Main]

[snip]

We don't know how long it will take to refuel, and since both the starship and the tanker can enter a higher orbit at the same time, Van Allen belts may not be such a problem if refueling will be fast.

Both the apogee-raise burn to HEEO and the departure burn are optimally performed at perigee, because Oberth. There are large performance losses (ie you can't reach the Moon) if you do it any other way.

There are much larger performance losses if you don't refuel at highly elliptic trajectory.

So? No one is arguing for that.

Argument that something should not be used unless it's perfect (when it's still much better than the alternatives) is stupid.

No one is arguing for that either. Also, rude.

And there is no problem of raising the apogee at pegiree, then having the whole ~20-hour orbit time to transfer the fuel, then burning for the moon on the next pegiree.

Needs to go through the Van Allen belts three times...

That is exactly the problem.

...not a big deal.

That's a value judgement. TheRadicalModerate and I are just pointing out the trade-off.

[Twark_Main]

(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. But yes, your point about refilling post-TMI is a good one.

[rakaydos]

(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. But yes, your point about refilling post-TMI is a good one.

it's only hyperbolic if the moon cuts off the orbit.

I've played enough kerbal to know you can have an orbit that wont inject to lunar SoI until the next time it goes around.

[Twark_Main]

(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. But yes, your point about refilling post-TMI is a good one.

it's only hyperbolic if the moon cuts off the orbit.

I've played enough kerbal to know you can have an orbit that wont inject to lunar SoI until the next time it goes around.

Right, it's hyperbolic if it's moving at greater than Earth escape velocity (eg Apollo). An elliptical trajectory increases the trip time, but it doesn't really save that much propellant.

[Paul451]

Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

"Don't you know that the Van Allen belts protect the Earth from solar storms? You corporate-lackey so-called 'scientists' only know how to destroy things." (Actual comments I've seen dominating the responses to articles about the VA belts on pop.sci sites.)

Isn't there also a way to drain at least the inner belt by injecting ELF from polar ground stations? (I might be misremembering, but I recall being amused by ELFs at the North Pole.)

[TheRadicalModerate]

(Technically, TLI is an HEEO...)

Technically it's hyperbolic, not elliptical. But yes, your point about refilling post-TMI is a good one.

TLI C3 is -2 km²/s², more or less.  Model it as about 200 x 380,000 km and you'll be pretty close.

For TMI, things are a lot easier, because there's no hope of taking enough prop with you to return (even though the hope of doing Sabatier ISRU with some martian water and CO2 is much higher).  You can put an SS into a shorter-than-Hohmann TMI, direct from LEO, no problem.  All this HEEO stuff is a lunar idiosyncrasy.

[wannamoonbase]

….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

[TheRadicalModerate]

….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...

[TrevorMonty]

….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...

While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

[Asteroza]

Or just use several micro-sats, with charged tethers, to drain the belts, and stop having to worry about it...

There is the classic Tethers Unlimited paper showing they can drain the belts with 10 small sats with charged tethers in a few weeks or so. But, who pays for it, and why? Because everyone benefits from it whether they paid in or not, especially GEO birds that slowly spiral orbit up to GEO with electric thrusters (since they avoid roasting their solar panels). One of those tragedy of the commons moments, best fixed by a multinational Space Guard service charged with keeping the spacelanes clear (space junk included). Though I could easily see SpaceX doing just because it was incidental to their ops.

https://web.archive.org/web/20190213154045/http://www.tethers.com/papers/ES_Remediation_IEEE_Paper.pdf

For a fuel depot service though, maybe cheat with equatorial LEO as the baseline as that's the lowest exposure? Though that doesn't help for other orbits...

[TheRadicalModerate]

….all this HEEO stuff is a lunar idiosyncrasy.

The HEEO and Lunar Gateway non-sense seems like NASA hedging itself.  That if lunar surface funds never arrived they would have a destination to use SLS and Orion.

If you're actually going to the Lunar surface then go to the surface.

If nobody's ever going to the lunar surface, then this really doesn't matter.  Personally, I'm guessing that 90% of the revenue that SpaceX will earn from BEO missions in this decade will come from lunar surface and cis-lunar missions.

Note that HEEO or TLI-based refueling is a solution to a Starship-specific problem, and has nothing to do with the Gateway.  The Gateway, on the other hand, is a sorta-kinda solution to a set of SLS/Orion/HLS sorta-kinda problems, and has nothing to do with HEEO.  (Gateway is basically a risk reduction measure, to ease assembly of the HLS components.  If Boeing has its way with the "whole lander/ascender on a separate Block 1B" proposal, the Gateway will go away.)

FWIW (and O/T), I'm a big proponent of replacing the SLS/Orion method of getting to the Gateway and back with using Starship as an LEO-to-Gateway-back-to-LEO shuttle.  This:

1) Doesn't require launching a crew with SH/SS.  They can board from a separately-launched (and crew-qualified) F9/D2.

2) Doesn't require landing SS on the lunar surface.  They can use the HLS components to do that.

3) Doesn't require reentering and landing a crew on Earth with SS.  SS can propulsively return to LEO, then re-board the D2 for reentry.

4) Requires only refueling in LEO, and requires zero refuelings with the crew on board.  If you've got Isp=375s, then you can get to NRHO and back to (propulsive) LEO with 1190 t of prop.

This gets rid of the expensive SLS and Orion components ASAP, because crew-qualifying a Starship for only in-space use is a lot easier than crew-qualifying for launch, reentry, or landing on the Moon.  So you start with this, using the Gateway and HLS to land on the Moon, then qualify the lunar landing segment, then the earth reentry, and finally the launch.

Of course, the real problem is that getting rid of the expensive SLS and Orion is exactly what Congress wants to avoid...

While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

If all Starship was ever going to do was an LEO-GW-LEO shuttle, I'd agree with you.  But the shuttle is merely the first capability, and the easiest one to get certified.  After that, SpaceX can bite off Earth EDL, followed by lunar landing/ascent, and finally launch from Earth with crew.  The order of these is up for debate, but the shuttle to and from NRHO is by far the lowest-hanging fruit.

[tbellman]

While I like idea of LEO-Gateway-LEO shuttle, SS is not best vehicle for this when only transferring few tons. Most of tanker missions fuel is used to move SS dry mass back and fore. A small purpose built shuttle could do round trip using 150 fuel, lot less if hydrolox.

Question is then, which such purpose-built shuttle?  When will that be available?  And will it be significantly cheaper than a twice-refuelled Starship (even if I don't believe the $2M/launch figure Elon envisions will be reached within that timeframe)?

My understanding is that ACES is not currently being developed.  Will Blue Moon or some auxillary part of New Glenn be able to shuttle back and forth between LEO and lunar/cis-lunar?  Any other crafts in development?