Author Topic: The likely future development program for Starship / Superheavy  (Read 20494 times)

Online lrk

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Just to be clear, I was suggesting that it would be best to land the first missions without relying on ground water as this has too many variables to stake the life of the crew on for the first few missions. The first few missions will be able to characterise the water deposits and experiment with different ways of accessing them. Follow up missions will be kitted out to exploit them.
That still borders on impracticality, if 10 tankers are needed to return one crew mission.  IMO, better to land one crew (with the capability to resupply them indefinitely) while they figure out how to make ISRU work.  Worst-case, it is still possible to send LH2 directly to allow easy ISRU in order to get them back. 

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Re kilopower, my understanding is that it uses Plutonium which is in very short supply so unlikely to be available in large quantities.
You are confusing kilopower with existing RTGs.  RTGs run off of radioactive decay heat from Pu-238, while kilopower uses high-enriched U-235, of which we have plenty from our stockpile and decommissioned nukes.  kilopower is actually safer than an RTG, since it doesn't become significantly radioactive until powered on for the first time, which would be after reaching Mars.  The biggest obstacle right now is regulatory, due to issues with handing HEU that could be used to make weapons if it falls into the wrong hands. 

Online Negan

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Just add external drop tanks until you have enough fuel to land (or get to LMO) Starship and get back to earth.

Edit: People just don't get the huge amount of flexibility you get when you have an extremely low mass to LEO cost.

Edit: Also don't understand why this wouldn't be a better option than loosing one ship plus making a special all vacuum raptor tanker that can't land on earth after coming back from Mars anyway.
« Last Edit: 12/21/2018 05:52 pm by Negan »

Online Slarty1080

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Just to be clear, I was suggesting that it would be best to land the first missions without relying on ground water as this has too many variables to stake the life of the crew on for the first few missions. The first few missions will be able to characterise the water deposits and experiment with different ways of accessing them. Follow up missions will be kitted out to exploit them.
That still borders on impracticality, if 10 tankers are needed to return one crew mission.  IMO, better to land one crew (with the capability to resupply them indefinitely) while they figure out how to make ISRU work.  Worst-case, it is still possible to send LH2 directly to allow easy ISRU in order to get them back. 

Quote
Re kilopower, my understanding is that it uses Plutonium which is in very short supply so unlikely to be available in large quantities.
You are confusing kilopower with existing RTGs.  RTGs run off of radioactive decay heat from Pu-238, while kilopower uses high-enriched U-235, of which we have plenty from our stockpile and decommissioned nukes.  kilopower is actually safer than an RTG, since it doesn't become significantly radioactive until powered on for the first time, which would be after reaching Mars.  The biggest obstacle right now is regulatory, due to issues with handing HEU that could be used to make weapons if it falls into the wrong hands.
Thanks for the clarification re the RTG / kilopower.

I think you misunderstand me on the landings. The proposal for 10 Starships is a totaly unworkable strawman argument. My proposal is for 3 Starships. A crewed SS, a tanker/cargo SS and an orbital tanker SS. The crewed SS refuels from the tanker/cargo SS in orbit (so no re-tanking required on th esurface). Both these SS land. After the mission the empty tanker/cargo SS is left on the surface, the crewed SS has enough propellant to reach low Mars orbit. Once there it can be re-tanked from the orbital tanker leaving both the crewed SS and the orbital tanker SS with enough propellant to return to Earth.
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Online lrk

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I'm curious if you have actually done the math for how much fuel will be required?  Not needing to re-launch some of your return fuel would definitely provide some benefit, but the initial accent to LMO requires several times as much dV as the burn from LMO to earth return.  Consequently I would be surprised if only one landing tanker is enough. 

Online Slarty1080

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I'm curious if you have actually done the math for how much fuel will be required?  Not needing to re-launch some of your return fuel would definitely provide some benefit, but the initial accent to LMO requires several times as much dV as the burn from LMO to earth return.  Consequently I would be surprised if only one landing tanker is enough.

You might be correct. It would be good to have someone look over the figures and assumptions that I made and we can pick the bones out of it...

   Dv        exh vel  massfract  drymass propcargo grossmass  propsreq
A 3600   3482     2.81         125        0              351           226
B 3400   3482     2.65         125        0              332           207
C 3400   3716     2.50         85          0              212           127
D 3800   3716     2.78         85          413          1385         1300

A Mars surface to LMO 200km (crew lift off)
B LMO to Earth SL raptors (crew return to Earth)
C LMO to LEO vac raptors (tanker return to Earth)
D LEO to LMO vac raptors (tanker full to Mars)
« Last Edit: 12/20/2018 01:56 am by Slarty1080 »
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Online Lar

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We have other threads where we have discussed which variants come first. The argument for Chomper is that it can be all the other variants. No other variant can be all the other variants since no other variant can be Chomper.

We have other threads where we discuss ISRU. I expect SpaceX to take an All In approach. Count on a Rodruigez well, drilled robotically, for the first two unmanned. The advantage of such as well is that it leaves gravel behind, only water and dissolved solids come up the pipe. You still need to distill the water feedstock to remove non water components, but you can do that with waste heat from the Sabatier.

If that doesn't work replan the next missions, but if it does, send people and 2 years of supplies knowing that if they can't get things running in two years, you THEN send a rescue mission with hydrogen or do the multi tanker approach.

Slarty1000, I think your LMO to earth is way low compared to mars surface to LMO.As someone else pointed out just before your post... But I am too lazy to dig up the cites for the actual numbers. Try the routemap thread.
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online Slarty1080

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We have other threads where we have discussed which variants come first. The argument for Chomper is that it can be all the other variants. No other variant can be all the other variants since no other variant can be Chomper.

We have other threads where we discuss ISRU. I expect SpaceX to take an All In approach. Count on a Rodruigez well, drilled robotically, for the first two unmanned. The advantage of such as well is that it leaves gravel behind, only water and dissolved solids come up the pipe. You still need to distill the water feedstock to remove non water components, but you can do that with waste heat from the Sabatier.

If that doesn't work replan the next missions, but if it does, send people and 2 years of supplies knowing that if they can't get things running in two years, you THEN send a rescue mission with hydrogen or do the multi tanker approach.

Slarty1000, I think your LMO to earth is way low compared to mars surface to LMO.As someone else pointed out just before your post... But I am too lazy to dig up the cites for the actual numbers. Try the routemap thread.

I think the surface to LMO value was too low thanks for that. I have increased that in line with the value from here: http://www.angelfire.com/md/dmdventures/orbitalmech/DeltaV.htm
Although it doesn't change the picture that much except the tanker/cargo SS can now only bring 90 tons of equipment instead of 100 tons.

Dv   exhV   MassFract   DryMass   PropCargo   GrossMass  PropReq
LEO to LMO  SL raptors (tanker/cargo)                    
3800   3482   2.98           175           320           1474           1299
LEO to LMO  SL raptors (crewed)                  
7250   3482   8.02           185           0           1484                1299
LEO to LMO vac raptors (orbital tanker)                  
3800   3716   2.78            85           413           1385              1300
                  
Surface to LMO (crewed)                  
4400   3482   3.54            125           0            442               317
LMO > Earth (crewed)                  
3400   3482   2.65            125           0            332               207
LMO to Earth (orbital tanker)                  
3400   3716   2.50             85           0            212               127

(tanker/cargo SS left on the surface)   

So I believe this is profile is possible, 3 Starships, one left on the surface no surface tanking no ISRU. As to whether it’s desirable or not that's another question.

I have been encouraged by some of the recent posts here that suggest the problem of accessing Martian water has at least in theory been solved using a Rodruigez well. I hope very much that this is the case and that robot Starships and other robotic craft sent ahead can prove this availability. Then it’s “just” a matter of sending lots of Starships with lots of power plant.

However if there are problems then this 3 Starship scenario could still be a fall-back position if boots are needed on the ground before ISRU is available. I think that probably is as far as we can get with this argument. Speculation as to desirability is not going to help much.

That still leaves my other questions however getting more back on topic:
Can they simply fit different front ends to a stub engine/tank body?
And how “legoesk” would it be to swap sea level raptors for vacuum raptors? 1 its easy or 10 it requires a total redesign / rebuild of the whole vehicle.
disclaimer - yes I know rockets are not lego elements - but I don't think I'm straining the development tool box too far here.
               

« Last Edit: 12/20/2018 06:44 pm by Slarty1080 »
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Online Negan

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Why bother with vacuum Raptors at all? How much extra payload will that give Starship?

Online Lar

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Why bother with vacuum Raptors at all? How much extra payload will that give Starship?
Quite a bit more IIRC. There are threads that estimate things like that, worth seeking out.

To LEO the payload is higher, since Starship arrives there with fairly close to empty tanks by design
To LMO you can load less fuel for a 25 tonne earth return payload since vacuum Raptors will do well on Mars where the surface atmo is a lot closer to vacuum than sea level.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online OneSpeed

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Why bother with vacuum Raptors at all? How much extra payload will that give Starship?

Here's a comparison between two 2017 BFS in LEO, both with an initial mass of 1335t, but with engines of 356 and 375 seconds of Isp respectively. If the final mass of the first is 235t, then for the same ∆V, the second ship can carry an extra 21.6t of payload. Feel free to download the attached zipfile containing the .NET program I used to do the calculation, and have a play with the numbers.

Online Negan

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So less than a 10% bump in payload to LEO if vacuum raptors are added.

Edit: Seems like people are trying to assume all vacuum Raptor version of Starship version. IMO that is pure fantasy.
« Last Edit: 12/21/2018 05:44 pm by Negan »

Online Lars-J

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So less than a 10% bump in payload to LEO if vacuum raptors are added.

Edit: Seems like people are trying to assume all vacuum Raptor version of Starship version. IMO that is pure fantasy.

Right. At most 4 engines would be replaced by Vacuum versions. The other three would remain sea level Raptors. An all Vacuum Raptor upper stage would have to be expendable, which is unlikely.

This is a great example of SpaceX optimizing for cost and practicality instead of extreme performance.
« Last Edit: 12/21/2018 06:17 pm by Lars-J »

Offline JonathanD

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An all Vacuum Raptor upper stage would have to be expendable, which is unlikely.

Unless they ultimately decided to have some sort of cycler approach for fast cargo delivery.  Chomper picks up cargo pod in LEO equipped with it's own Mars EDL system, dumps it off at Mars where it lands on the surface.

Certainly makes for a complicated cargo pod, but if it was designed for one landing on Mars like NASA payloads are, it would simplify things (could use cheaper ablative heat shield, 1-time use solid retro rockets and such).  And then the Cargo Chomper Cycler (CCC anyone?) could be greatly optimized for fast trips between Earth and Mars orbits (all vacuum engines, no TPS, landing legs, minimal aero bits, big gas tank for more aggressive transfer time, etc.).

Online Slarty1080

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So less than a 10% bump in payload to LEO if vacuum raptors are added.

Well it all adds up. Packing as much as possible into a cargo SS on the slow trajectory to Mars also helps a great deal, then there's the possibility at some point of pushing the 300bar pressure up a little and probably other changes.

Hence one of my questions - how difficult would it be to convert a SS to 7vac raptors or 4sl 3vac? This question is aimed directly at the whole point of this thread which is about future versions of SS. If it's relatively easy then it might be worth the effort.

That said I suppose vacuum raptors might pose a landing issue (large and flimsy) and also compromise engine failure fault tolerance? If that’s the case then we are unlikely to see the vacuum raptor in the near future if ever.

This would imply that there will only ever be one version of SS from an engine layout perspective. And version changes would then be down to TPS changes, engine upgrades (300+bar or similar mods) and the usual myriad of tweaks to save weight or improve reliability.

Then there's the chomper v cargo v crew version issue and whether they can overcome this by swapping out the nose as required? In this scenario one engine/ tank assembly could fly as a chomper on one flight and as a crew carrier on another. Possible? Likely? Why?

One further point to throw in how will a tanker version be implemented?
 a) A dedicated version with stretched tanks and or a modified outer mould line. Optimising carrying capacity but also maximising configurational change?
 b) Design the standard Starship with slightly oversized tanks so that a tanker can be built by simply omitting the decks, crew and cargo and tanking up to capacity. Suboptimal capacity for standard Starships, but minimised configurational change for tankers?
 c) Leave the standard Starship as is and when  a tanker version is wanted just leave out the decks, crew and cargo and install additional tankage in the nose end (with pipework to connect these tanks to the main tanks) to hold the extra propellant?
d) Use the standard Starship as a tanker just carrying 100tons of propellant?

Or some other arrangement? They will need a lot of tankers as soon as they start up the deep space / Mars missions.
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Online Slarty1080

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An all Vacuum Raptor upper stage would have to be expendable, which is unlikely.

Unless they ultimately decided to have some sort of cycler approach for fast cargo delivery.  Chomper picks up cargo pod in LEO equipped with it's own Mars EDL system, dumps it off at Mars where it lands on the surface.

Certainly makes for a complicated cargo pod, but if it was designed for one landing on Mars like NASA payloads are, it would simplify things (could use cheaper ablative heat shield, 1-time use solid retro rockets and such).  And then the Cargo Chomper Cycler (CCC anyone?) could be greatly optimized for fast trips between Earth and Mars orbits (all vacuum engines, no TPS, landing legs, minimal aero bits, big gas tank for more aggressive transfer time, etc.).

Yes an all vac raptor Starship would have to remain in space. Certainly not an immediate option, but might be useful to maximise cargo availability in LMO
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Online Negan

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So less than a 10% bump in payload to LEO if vacuum raptors are added.

Packing as much as possible into a cargo SS on the slow trajectory to Mars also helps a great deal

Looking at the changes from the 2017 to 2018 version, they are more worried about volume constraints than mass.
« Last Edit: 12/21/2018 07:27 pm by Negan »

Online Negan

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Looking at the SpaceX Mar's webpage, satellites will be deployed with the chomper version. The following is the first description listed under "Starship Uses":

"SpaceX's Starship and Super Heavy rocket are designed to deliver satellites to Earth orbit and beyond, at a lower marginal cost per launch than our current Falcon vehicles. With a 9m diameter forward payload compartment, larger than any other current or planned fairing, Starship creates possibilities for new missions, including space telescopes even larger than the James Webb."

IMO it will be one of the first Starships made.
« Last Edit: 12/21/2018 07:00 pm by Negan »

Online Cheapchips

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Missions that we already know about (Starlink, dearmoon, Mars cargo) don't need Chomper.  I don't see why you'd go first with it.

The 2017 design didn't look to me like a universal starting point for other variants. It looked like the angled base of the door would cut through where the cargo doors are.

Offline Cinder

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Missions that we already know about (Starlink, dearmoon, Mars cargo) don't need Chomper.  I don't see why you'd go first with it.
You would have to refute this argument:
The argument for Chomper is that it can be all the other variants. No other variant can be all the other variants since no other variant can be Chomper.
Warning - while you were reading 86 new replies have been posted. You may wish to review your post.

Offline KelvinZero

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So less than a 10% bump in payload to LEO if vacuum raptors are added.
I think it looks more impressive if you don't include the 80-ish tons dry mass of the Starship as payload.

155 tons of cargo without vacuum raptors
176.6 tons of cargo with vacuum raptors.

so that is 21.6 tons more cargo, or 114% the cargo of the non-vac version. If the mass of the Starship crept up even further vac-raptors would begin to look better still, eg +20% if the non-vac was 100t cargo.

For sure, it does not look important for early versions, just a possible optimisation for later.