Starship On-orbit refueling - Options and Discussion

[Twark_Main]

The numbers would be interesting if only to suggest the utility of this optimization. There are a wide range of other as yet undefined impacts that might favor fast or slow transfer.


Assume a Mars bound ship needing four tanker loads. One option is to launch one tanker every 24+/- hours. This would allow but not necessarily demand a slow transfer. Another option is to launch two each from BC and the Cape and have them queue up awaiting their turn. This would almost but not quite demand a fast transfer.


If the depot has great thermal control and the tankers don't, fast transfer with either option looks good. At the other extreme, if neither has good thermal control slow may be the only savings to be found. Then there's everything in between.


And there's other issues. High vs low beta and pad availability being two variables that come to mind.


As you say, building the model to apply the math to is the hard part.


A note on the plumbing. With absolutely no proof, I think it was designed to service a stacked ship at one g. We (and probably SX too) don't know with absolute certainty that this plumbing will be used for transfer. I'm sure it'll be tested first but well, this is SpaceX we're talking about.

Yeah, the "nothing left to take away" solution is to not increase the size of the plumbing, and just use that to back-calculate the filling rate.

Here you can plug in a few different thermal options, and choose the option that gives the lowest cost per unit of propellant upmass.

Afterwards you always have the option to do the partial derivative on the plumbing mass and propellant loss. I expect with a sub-cooled depot it won't be worth upsizing the plumbing, however. 

I think that fully constrains the optimization problem in the forward direction.... 

[mikelepage]

Using the Super Heavy as the fuel depot is really an underexplored idea. 

Using the mass and ISP numbers from Wikipedia (who knows if they're any good) the Super Heavy is on the cusp of SSTO if it were flown without a starship/payload.  <snip>

Having the capacity to store two SS worth of fuel <snip>

I was playing with my calcs from the Simplified Mission Architecture thread, and tested whether using SH converted to depot - then used in a nose-to-tail config as the Starbooster/Starpusher "stage 1" during TLI, allows HLS to make it to lunar surface and back without post-ascent refuelling. It gets you to TEI, but then you run into the problem of the lack of aero-surfaces on HLS returning to LEO.

It's hard to get away from how *useful* a post-lunar-ascent top-up of propellant is. 250t of extra prop post lunar ascent allows HLS to propulsively brake into LEO, where crew can transfer to whatever EDL craft is preferred.

One of the main problems with the lunar tanker idea is that has always been that it would require a whole separate depot and refuelling campaign to get it to the moon, completely separate from HLS.

Well, what if it doesn't?

SuperHeavy as SSTO depot could store more than 2x SS worth of fuel. For this argument it doesn't matter whether we use the probe-drogue or nose-to-tail docking.

1) Tanker campaign to refuel SuperHeavy Depot.
2) Final tanker (standard cargo model with aero-surfaces) docks with SH Depot for prop transfer, then performs TLI to LLO.
3) HLS docks with SH Depot to get rest of prop, then performs TLI to LLO.
4) Surface landing, mission, launch and top-up from waiting tanker.
5) Both HLS and tanker perform TEI, tanker aerobrakes, while HLS brakes propulsively into LEO.
6) Crew transfer to capsule and EDL.

Spreadsheet attached.

Side note 1: if crew is already on HLS when receiving prop from depot, it would mean both tanker and HLS wouldn't be so tightly constrained to milli-G acceleration during prop transfer, as that would just be energy towards TLI. Not necessary though.

Side note 2: Using a chine-deployed solar-array as shield on SH-depot could allow you to shade the tanks in LEO, but I realised I called it an Earth-shield in a previous post. A better orientation (I think) would be to make it a sunshield + solar array, then point the depot axis at Earth to minimise Earthshine.

EDIT: Have re-uploaded spreadsheet to correct a dry-mass mistake I made. The mission does still close, although there's no longer anything in the way of sandbagging for propellant boil off during the lunar mission.

[DanClemmensen]

What does SpaceX call their side-by-side docking scheme?

I was using "quad probe-and-drogue", But I changed to "quad probe-and-socket" because a "drogue" is historically something dragged on a flexible line behind a ship or aircraft, like the fuel connector deployed behind a Navy tanker aircraft, or a small parachute, or a small sea anchor.

However, the word got misused to describe the fixed receiving interface of certain spacecraft docking systems, which absolutely do not dangle on a flexible connection.

[catdlr]

What does SpaceX call their side-by-side docking scheme?

I was using "quad probe-and-drogue", But I changed to "quad probe-and-socket" because a "drogue" is historically something dragged on a flexible line behind a ship or aircraft, like the fuel connector deployed behind a Navy tanker aircraft, or a small parachute, or a small sea anchor.

However, the word got misused to describe the fixed receiving interface of certain spacecraft docking systems, which absolutely do not dangle on a flexible connection.

After naming the Pad-2 hold down tester "Ibeproofin", he'll come up with some "banger" name for the docking.

[OTV Booster]

Using the Super Heavy as the fuel depot is really an underexplored idea. 

Using the mass and ISP numbers from Wikipedia (who knows if they're any good) the Super Heavy is on the cusp of SSTO if it were flown without a starship/payload.  <snip>

Having the capacity to store two SS worth of fuel <snip>

I was playing with my calcs from the Simplified Mission Architecture thread, and tested whether using SH converted to depot - then used in a nose-to-tail config as the Starbooster/Starpusher "stage 1" during TLI, allows HLS to make it to lunar surface and back without post-ascent refuelling. It gets you to TEI, but then you run into the problem of the lack of aero-surfaces on HLS returning to LEO.

It's hard to get away from how *useful* a post-lunar-ascent top-up of propellant is. 250t of extra prop post lunar ascent allows HLS to propulsively brake into LEO, where crew can transfer to whatever EDL craft is preferred.

One of the main problems with the lunar tanker idea is that has always been that it would require a whole separate depot and refuelling campaign to get it to the moon, completely separate from HLS.

Well, what if it doesn't?

SuperHeavy as SSTO depot could store more than 2x SS worth of fuel. For this argument it doesn't matter whether we use the probe-drogue or nose-to-tail docking.

1) Tanker campaign to refuel SuperHeavy Depot.
2) Final tanker (standard cargo model with aero-surfaces) docks with SH Depot for prop transfer, then performs TLI to LLO.
3) HLS docks with SH Depot to get rest of prop, then performs TLI to LLO.
4) Surface landing, mission, launch and top-up from waiting tanker.
5) Both HLS and tanker perform TEI, tanker aerobrakes, while HLS brakes propulsively into LEO.
6) Crew transfer to capsule and EDL.

Spreadsheet attached.

Side note 1: if crew is already on HLS when receiving prop from depot, it would mean both tanker and HLS wouldn't be so tightly constrained to milli-G acceleration during prop transfer, as that would just be energy towards TLI. Not necessary though.

Side note 2: Using a chine-deployed solar-array as shield on SH-depot could allow you to shade the tanks in LEO, but I realised I called it an Earth-shield in a previous post. A better orientation (I think) would be to make it a sunshield + solar array, then point the depot axis at Earth to minimise Earthshine.

A note on side note 2. The sun covers a half degree of sky. Either tail orientation or shield could handle this. Earth OTOH, covers a big wad of sky. No way a tail orientation could cover it all.


As a guess, I'd say that specular ocean reflection is the worst of it and tail first could most likely handle this at the cost of missing everything else.


My gut says this is a bad thermal trade but does not address other possible thermal treatments or structural and operational issues.


Beyond side note 2: Great stuff.

[OTV Booster]

What does SpaceX call their side-by-side docking scheme?

I was using "quad probe-and-drogue", But I changed to "quad probe-and-socket" because a "drogue" is historically something dragged on a flexible line behind a ship or aircraft, like the fuel connector deployed behind a Navy tanker aircraft, or a small parachute, or a small sea anchor.

However, the word got misused to describe the fixed receiving interface of certain spacecraft docking systems, which absolutely do not dangle on a flexible connection.

After naming the Pad-2 hold down tester "Ibeproofin", he'll come up with some "banger" name for the docking.

Missionary Mating?

[jarmumd]

What does SpaceX call their side-by-side docking scheme?

I was using "quad probe-and-drogue", But I changed to "quad probe-and-socket" because a "drogue" is historically something dragged on a flexible line behind a ship or aircraft, like the fuel connector deployed behind a Navy tanker aircraft, or a small parachute, or a small sea anchor.

However, the word got misused to describe the fixed receiving interface of certain spacecraft docking systems, which absolutely do not dangle on a flexible connection.

There may be someone who is really hung up on the nomenclature, but I tend to use Probe with Cone or Drogue interchangeably.  Socket is a bit confusing with the umbilical plugs/sockets.

[meekGee]

What does SpaceX call their side-by-side docking scheme?

I was using "quad probe-and-drogue", But I changed to "quad probe-and-socket" because a "drogue" is historically something dragged on a flexible line behind a ship or aircraft, like the fuel connector deployed behind a Navy tanker aircraft, or a small parachute, or a small sea anchor.

However, the word got misused to describe the fixed receiving interface of certain spacecraft docking systems, which absolutely do not dangle on a flexible connection.

After naming the Pad-2 hold down tester "Ibeproofin", he'll come up with some "banger" name for the docking.

Ibebanging. You already had it. 

[Twark_Main]

I'm not convinced that SpaceX has made a final decision on on-orbit docking. We [...] have seen a little bit of hardware [...] Maybe they are still looking at alternatives. In particular, nose-to-tail docking may still be in the running.

I think you are reaching. The current scheme is the simplest, it fits SpaceX's MO exactly (using the existing QD). I'd expect they are treating it as the only option until slapped hard in the face with a show-stopper.

I'm sure they are aware of other possibilities. Nose-tail, nose-nose, tail-tail, nose-dorsal-90-degrees, spin, no-spin, etc etc. If I can think of it, they certainly can. But pretending that your preferred toy model is still on the table at this point is just wishful thinking, IMO.

Could've said the same about stainless steel after SpaceX showed that huge CF mandrel.

To dock the nose of a Depot to the tail of another ship, the Depot nose could use a 6DOF soft-dock ring similar to the IDSS soft-dock but 9 meters in diameter.

I can't see this working. Starship's nose is about 13-14m long, say 12m to reach the opposite ring hardware. Assuming the soft-dock interstage-ring hybrid is around 2m, that means you need six 10m long extendable struts.

I think this is the least ingenious way to imagine "scaling up" an IDSS, ie essentially MSPaint.exe stretching the entire thing.

If you're more clever you realize that the positional error doesn't actually scale up with the size of the docking ring, so you can keep the alignment petals of a similar size and just spread them apart, distributed around the perimeter. You may only need to double up the alignment ramp surfaces at each location.

Plus a receiving ring around the engine skirt of the other ship with all the clamping hardware. Plus you need entirely new plumbing on both ships.

One of the great parts is that you can reuse / adapt that from the existing clamps and skirt, instead of having to re-invent this in duplicate  for side-by-side docking.

Some new plumbing? Of course. Entirely new plumbing? Of course not.

Plus you need to add the extendable docking ring to the nose of the depot after launch, which means....

"Weaponized incompetence"

Oh good. Social media has taught you a new way to belittle people. Just what we needed.

Social media certainly has thrown light on that "debate" tactic (or should it be "shut down debate" tactic  )

To summarize where we left off technically, you don't need some completely separate docking ring and attachment procedure (you just modify the existing docking ring), and you don't need to replace all the plumbing, and you don't need some comically-sized IDSS petals.



What do you need? A refilling arm that folds up flat against the side of the rocket for launch would be nice, using similar flexible joints as the Raptor engines.

This would keep the tanks even better protected during docking, because you can pull away the arm into a "ready to dock" position that's as far from the thin tank wall as desired.

Is a nose cone necessary for launch? Or merely a fairing over the arm? Or nothing and just add a thermal coating? 

[OTV Booster]

Using the Super Heavy as the fuel depot is really an underexplored idea. 

Using the mass and ISP numbers from Wikipedia (who knows if they're any good) the Super Heavy is on the cusp of SSTO if it were flown without a starship/payload.  <snip>

Having the capacity to store two SS worth of fuel <snip>

I was playing with my calcs from the Simplified Mission Architecture thread, and tested whether using SH converted to depot - then used in a nose-to-tail config as the Starbooster/Starpusher "stage 1" during TLI, allows HLS to make it to lunar surface and back without post-ascent refuelling. It gets you to TEI, but then you run into the problem of the lack of aero-surfaces on HLS returning to LEO.

It's hard to get away from how *useful* a post-lunar-ascent top-up of propellant is. 250t of extra prop post lunar ascent allows HLS to propulsively brake into LEO, where crew can transfer to whatever EDL craft is preferred.

One of the main problems with the lunar tanker idea is that has always been that it would require a whole separate depot and refuelling campaign to get it to the moon, completely separate from HLS.

Well, what if it doesn't?

SuperHeavy as SSTO depot could store more than 2x SS worth of fuel. For this argument it doesn't matter whether we use the probe-drogue or nose-to-tail docking.

1) Tanker campaign to refuel SuperHeavy Depot.
2) Final tanker (standard cargo model with aero-surfaces) docks with SH Depot for prop transfer, then performs TLI to LLO.
3) HLS docks with SH Depot to get rest of prop, then performs TLI to LLO.
4) Surface landing, mission, launch and top-up from waiting tanker.
5) Both HLS and tanker perform TEI, tanker aerobrakes, while HLS brakes propulsively into LEO.
6) Crew transfer to capsule and EDL.

Spreadsheet attached.

Side note 1: if crew is already on HLS when receiving prop from depot, it would mean both tanker and HLS wouldn't be so tightly constrained to milli-G acceleration during prop transfer, as that would just be energy towards TLI. Not necessary though.

Side note 2: Using a chine-deployed solar-array as shield on SH-depot could allow you to shade the tanks in LEO, but I realised I called it an Earth-shield in a previous post. A better orientation (I think) would be to make it a sunshield + solar array, then point the depot axis at Earth to minimise Earthshine.

EDIT: Have re-uploaded spreadsheet to correct a dry-mass mistake I made. The mission does still close, although there's no longer anything in the way of sandbagging for propellant boil off during the lunar mission.

The more I think about using the booster as a depot and docking nose to tail, the more I like it. Not for the immediate future but maybe 5-10 years down the road. In the short term SX needs to get something, anything, working to meet external obligations and internal goals. Something just good enough, which looks like what they've been rendering.

The HSR (Hot Stage Ring) looks like its almost half way to being a 6 DOF whatchamacallit platform. Twarks extension arm to the SQD would work for fluid transfer. Shades, solar panels, cryo coolers and radiators might be fit into fairings or be carried in an added space above the top dome and below the coupling ring, or some combo. 

Because the GP (General Purpose) depot would most likely have to periodically raise orbit, and SP (Special Purpose) depots might have to rise up to HEEO or some flavor of lunar orbit, it would be nice if most of the engines could be removed. We can leave that for the 10 year projection but it does raise an issue. Personal rant to follow.

I am strongly of the opinion that extensive infrastructure is the key to human expansion into space. Not like the ISS, which is a destination, but like the depot which directly supports further activity. Imagine Eisenhower's 1919 odyssey across the continent with vehicles of the time but good highways, repair facilities, gas stations, restaurants, C stores and hotels or campsites with facilities. It would have been a whole different thing, and directly attributable to infrastructure.

A depot as envisioned or of any sort, is a move in this direction. It will morph a good idea into hands on nuts and bolts experience which when combined with increasing economic activity in space will justify more complex infrastructure. V1 might only be used for a few transfers before being splashed but V2 will most likely be seen as a valuable piece of long term infrastructure. Design elements that make no sense for V1 would be viable.

When the IRS lists propellant depots as 30 year properties we'll know we're there.

/end rant

[Tywin]

So now more delays, the refueling demo, now is for 2027?!

[meekGee]

So now more delays, the refueling demo, now is for 2027?!

Aren't you at the "Musk isn't going to Mars" party?  What's the point of your useless post? 

Do you know anyone else planning on refueling flights before then?

[Tywin]

So now more delays, the refueling demo, now is for 2027?!

Aren't you at the "Musk isn't going to Mars" party?  What's the point of your useless post? 

Do you know anyone else planning on refueling flights before then?

What have to do with Mars, this is important for the HLS, remember?

[meekGee]

So now more delays, the refueling demo, now is for 2027?!

Aren't you at the "Musk isn't going to Mars" party?  What's the point of your useless post? 

Do you know anyone else planning on refueling flights before then?

What have to do with Mars, this is important for the HLS, remember?

What's the point bemoaning whether it's the end of 2026 or beginning of 2027?

It will happen faster than any other option, somewhere around 2026/7.  Kinda depends on how well the first flights go.