Wiki Super Heavy/Starship - General Development Discussion

[FoverM]

First off, SpaceX is working on a lunar version with neither fins nor heat shield, but including higher mounted engines for landing/ takeoff. So lunar surface to earth surface isn't a design constraint.

I thought SS was going to do everything? Now they're talking about customized versions for specific environments???

Have you done the math on landing and returning ~100 mT dry mass from the lunar surface to NRHO? You're going to need beefy engines to land successfully. To prevent debris from scattering into the skirt like in a recent SS test, they'll need to be high up. Are they going to be gaseous or liquid? In addition, round-tripping that much dry mass will require a bunch of propellant (we haven't even started talking about delivered payload!). How much propellant can be delivered to NRHO by a single fully-fueled SS tanker in LEO?

Why is required mass/ fuel load ugly? Fuel is the least expensive part of the entire endeavor (once all the other pieces are reusable). At two million dollars a launch (2019 Elon estinate) for a refueling run, even a dozen trips (if SS needed totally full tanks) is only $24 million. That is about the cost of four sets of F9 fairingsn about the cost of reused F9 launch ($50 million). Other than requiring more fuel, what's the problem?

What's the schedule for launching up to a dozen tanker missions to complete one successful BEO mission? How much propellant will you lose to boil-off during that time?

I'd rather SpaceX spend their time and talent on designing innovative in-space craft that handle the Earth->Moon task.

 

[mongo]

I thought SS was going to do everything? Now they're talking about customized versions for specific environments???

It has always been known SS had variants: sattelite, human, and tanker. Lunar is a variation on that theme:
SS - fins and tiles + upper level engines

Have you done the math on landing and returning ~100 mT dry mass from the lunar surface to NRHO? You're going to need beefy engines to land successfully. To prevent debris from scattering into the skirt like in a recent SS test, they'll need to be high up. Are they going to be gaseous or liquid? In addition, round-tripping that much dry mass will require a bunch of propellant (we haven't even started talking about delivered payload!). How much propellant can be delivered to NRHO by a single fully-fueled SS tanker in LEO?

Done via phone and websites, may have errors:

Moon to LLO: 1760
Moon to GTO: 3260
Moon to LEO: 5660

Vacuum raptor: 380 s
Max fuel mass: 1200 metric tons
Dry mass: 100 mT
Payload: 100 mTon max

From LEO, 11320 m/s is needed round trip. Assuming lunar landing mass = lunar takeoff mass, that puts final mass at 67 mT, too light. So you can't do that trip.

SS delta-V with full payload and fuel: 7246 m/s
One way: 3623m/s
This is sufficient to round trip from GTO to the surface and back. Not that you need to take 100 metric tons to the surface, nor, having done so, would you bring all 100 tons back.

LEO to GTO is 2440 m/s
A fully loaded LEO SS tanker can get
727 mT to GTO and needs to be at
193 mT to return to LEO
Net fuel transfer: 530 mT
SS itself would weigh in at 727 mT once in GTO, so one GTO refill puts it at near max fuel load: 1257 mT (143 mT light)
This fuel load corresponds to a return to GTO mass of 218 mT which is full payload to and from the moon with some fuel left. A partial topoff gets it back to LEO.

Total LEO-GTO trips:
2 tanker
1 human lunar

Earth to LEO launches:
1 human lunar
1 human earth (or dragon)
<36 Earth tankers (fill 2nd tanker, and use on the next flight).

Total ships needed:
2 tankers
1 human lunar
1 human earth (unless dragon is used)

Not sure on the landing engine tech, I'd expect liquid fed methalox for commonality.

What's the schedule for launching up to a dozen tanker missions to complete one successful BEO mission? How much propellant will you lose to boil-off during that time?

With only one launch site, but extra tankers: it would either be 12 days for direct to plane, or less with plane shifting. Full tankers can be prestaged for minimal crew time in orbit.

I don't think fuel boil off is not a huge issue since it is only radiative heating. The Mars trip would experience more of that then a lunar excursion. In either case, ship attitude can minimze solar heating and micro acceleration can keep fuel off the sunward surfaces. In a reverse spinnaker type setup, the solar panels could act as a shield (at a minimum a radiator on the dark side)

I'd rather SpaceX spend their time and talent on designing innovative in-space craft that handle the Earth->Moon task.

What's the ROI for optimizing Earth->Moon transportation?

 

[Cosmacelf]

I'd rather SpaceX spend their time and talent on designing innovative in-space craft that handle the Earth->Moon task.

Do you realize how much R&D $$ it will cost for SpaceX to do anything related to earth-moon and earth-mars? More than even the seemingly unlimited supply of private investment capital, I'm sure. So if the US Govt is willing to shove billions of R&D $$ SpaceX's way for R&D that SpaceX can then mostly reuse for their Mars mission, they'll gladly take it.

 

[scaesare]

Apologies if I've missed the answer to this somewhere, but we know that SN'8 was running engine-rich upon landing due to fuel delivery issues from the header tank. Has there been any further discussion of why that was the case? (and therefore what would need to be done to address it for SN9?).

 

[ItsNotAboutTheMoney]

Since they're also building a solar farm, they could be using the desalinated water for making synthetic methane too.

And maybe some Tesla Roadrunners mentioned that desalination plant brine is mineral rich.

 

[HVM]

Apologies if I've missed the answer to this somewhere, but we know that SN'8 was running engine-rich upon landing due to fuel delivery issues from the header tank. Has there been any further discussion of why that was the case? (and therefore what would need to be done to address it for SN9?).

Here is detailed explanation of situation and fixes:

https://twitter.com/elonmusk/status/1341916523288555520

 

[HVM]

Elon:
"We’re going to try to catch the Super Heavy Booster with the launch tower arm, using the grid fins to take the load"

Apologies if I've missed the answer to this somewhere, but we know that SN'8 was running engine-rich upon landing due to fuel delivery issues from the header tank. Has there been any further discussion of why that was the case? (and therefore what would need to be done to address it for SN9?).

"SN9 will press CH4 header tank with helium. Long-term solution is under debate. Not clear what is lightest/simplest."

https://twitter.com/elonmusk/status/1344344855237992448

 

[ICUDoc]

"We're going to try to catch the Super Heavy Booster with the Launch Tower arm, using the grid fins to take the load"
That is one of the most astounding sentences I've ever read....
What an amazing time to be alive.

 

[favo]

Well, this will certainly be exciting! (More tweets follow...)

Elon Musk @elonmusk
Replying to @flcnhvy and @ErcXspace

Saves mass & cost of legs & enables immediate repositioning of booster on to launch mount — ready to refly in under an hour
1:00 PM · Dec 30, 2020·Twitter for iPhone

[...]

Viv @flcnhvy
Also, what implications does this have for droneship landings? Or will all Starship droneships essentially be fully fledged ocean spaceports, including launch mount?

Elon Musk @elonmusk
Replying to @flcnhvy and @ErcXspace
Yes
1:00 PM · Dec 30, 2020·Twitter for iPhone

[...]

James Stephenson @ICannot_Enough
So, the launch stand would catch the booster by the grid fins... the same way a dad might catch a kid they just threw in the air??

Aloysius Fekete @AloysiusFekete
Grid fins already built to extend and resist high forces. They don't have shock absorption. But, I suppose this could be built into the tower. So net reduction in rocket complexity and weight.

James Stephenson @ICannot_Enough
Yeah, you could build shock absorbers into the launch stand’s arms without having to worry about any weight penalty.

Elon Musk @elonmusk
Replying to @ICannot_Enough @AloysiusFekete and 3 others

Exactly
1:18 PM · Dec 30, 2020·Twitter for iPhone

[edited to add:]

Elon Musk @elonmusk
Replying to @Erdayastronaut
Might be a few lumps along the way

2:49 PM · Dec 30, 2020·Twitter for iPhone

 

[ICUDoc]

Might be a few lumps along the way

What a ride this will be- literally and figuratively

 

[scaesare]

Elon:
"We’re going to try to catch the Super Heavy Booster with the launch tower arm, using the grid fins to take the load"
View attachment 622512

"SN9 will press CH4 header tank with helium. Long-term solution is under debate. Not clear what is lightest/simplest."

https://twitter.com/elonmusk/status/1344344855237992448

Thanks @HVM ... now I'm with the other folks who are marveling at the idea of the idea of the tower being able to grab the Super Heavy Booster.

The precision necessary for that would seem astounding...

 

[mongo]

Thanks @HVM ... now I'm with the other folks who are marveling at the idea of the idea of the tower being able to grab the Super Heavy Booster.

The precision necessary for that would seem astounding...

The arms will swing, so less precision is needed than a fixed cradle. Given the good first stage roll control, the system will be able to maneuver in under two opposing fin mounts.
If the arms are mounted to vertical slides on the tower with dampers, then there is no lateral motion induced during vertical displacement. As opposed to a fixed pivot and shock absorber brace.

The tower crane can be used to grab and reposition the stage on the mount, so no need for much in the way of arm extension/ retraction features. That simplifies things and allows the arms to be more engine blast resistant.

 

[FoverM]

So we're already running into trouble landing the SH, which doesn't carry people and therefore is less critical. What does that say about SS which will supposedly carry people??? The SS landing legs/system need to work on the Earth, Moon, and Mars and can carry, what, 100 mT payload to each destination?

Musk needs to partition his team into an Earth-LEO-Earth segment and then a LEO-wherever-LEO segment (to start with). The Earth-LEO-Earth segment is at least half the problem. Just look at the delta-V requirements.

 

[mongo]

So we're already running into trouble landing the SH, which doesn't carry people and therefore is less critical. What does that say about SS which will supposedly carry people???

Who said anything about running into trouble? They are working on the next step of optimization (before the first one is even built).
F9 already lands the first stage, what does that say about landing SH or SS?

The SS landing legs/system need to work on the Earth, Moon, and Mars and can carry, what, 100 mT payload to each destination?

100mT is the LEO SS capacity, no reason they must maintain that for landings.
The HSL program payload requirements (including crew) are for less than 1mT to the surface (865kg min, 965 goal) and <1mT back up to Lunar orbit (525kg). Plus 8 days of life support.

Musk needs to partition his team into an Earth-LEO-Earth segment and then a LEO-wherever-LEO segment (to start with). The Earth-LEO-Earth segment is at least half the problem.

If you have Earth-LEO-Earth (with human and tanker variants), then you already have LEO-wherever-LEO. LEO-wherever-LEO also needs to do wherever-surface-wherever and w-s-w must refuel the LEO-wherever-LEO, unless the LEO-wherever-LEO craft carries all return fuel with it, or enough to refuel the one use wherever-surface-LEO craft, in which case it was only a LEO-wherever craft...

Just look at the delta-V requirements.

I did: Falcon Super Heavy/Starship - General Development Discussion

And they get even easier if lunar SS are left there as habitation (part of the new base). Plenty of cargo space for an ascent vehicle. Not that physics requires it.

 

[scaesare]

The arms will swing, so less precision is needed than a fixed cradle. Given the good first stage roll control, the system will be able to maneuver in under two opposing fin mounts.
If the arms are mounted to vertical slides on the tower with dampers, then there is no lateral motion induced during vertical displacement. As opposed to a fixed pivot and shock absorber brace.

The tower crane can be used to grab and reposition the stage on the mount, so no need for much in the way of arm extension/ retraction features. That simplifies things and allows the arms to be more engine blast resistant.

Still... If I'm envisioning this in my mind correctly[1], we are talking some pretty tight tolerances for a maneuver like that it would seem.

The Falcon 9 is ~3.7m diameter. Based on the pics of the fins as compared to the workers, I'd say their length is roughly half that.

So if the 50% fin-length to booster-diameter ration holds, that makes the SH fins ~4.5m as compared to the 9m dia. booster.

For the cradle mechanism would have to allow maximum lateral variation in booster position, the cradle arms would have to be positioned at about the kid-way point of each grid fin. Any farther apart and you risk the booster "slipping though" on one side. Much closer together, and you limit the amount of imprecision you can tolerate.

So that means 0.5 x 2.5m - 2.25m of lateral variation that the combined rocket + swinging cradle can tolerate. For a 9 x 70m booster coming in hot and containing explosive fuel mixtures, this is gonna be fun to watch!! [2]

-sc

[1] I'm thinking old-school candle-stick telephone receiver and cradle:

[2] I'm looking forward to the "How Not to Catch an Orbital-Class Super-Heavy Rocket" youtube reel...

 

[mongo]

Still... If I'm envisioning this in my mind correctly[1], we are talking some pretty tight tolerances for a maneuver like that it would seem.

The Falcon 9 is ~3.7m diameter. Based on the pics of the fins as compared to the workers, I'd say their length is roughly half that.

So if the 50% fin-length to booster-diameter ration holds, that makes the SH fins ~4.5m as compared to the 9m dia. booster.

For the cradle mechanism would have to allow maximum lateral variation in booster position, the cradle arms would have to be positioned at about the kid-way point of each grid fin. Any farther apart and you risk the booster "slipping though" on one side. Much closer together, and you limit the amount of imprecision you can tolerate.

So that means 0.5 x 2.5m - 2.25m of lateral variation that the combined rocket + swinging cradle can tolerate. For a 9 x 70m booster coming in hot and containing explosive fuel mixtures, this is gonna be fun to watch!! [2]

-sc

[1] I'm thinking old-school candle-stick telephone receiver and cradle:

[2] I'm looking forward to the "How Not to Catch an Orbital-Class Super-Heavy Rocket" youtube reel...

I'm not thinking a cradle, that would be one arm.
I'm envisioning two independent arms that each pivot and cover a near 180 degree region extending out their length. (90 degrees to tower being ideal).
They track the booster's entry and swing into position as it passes by.
Black: tower
Blue: arms
Orange: capture area

Not really any tolerances, critcal parameters are arm manuvering speed and accuracy versus booster lateral speed.
Optionally, the fins can move to an angled downward position to grab the arms and tuck them in. Other pair should be folded for clearance.

For fun, imagine holding the rocket by all four points for launch. Can then be high off the ground, and the base never needs to support a fully fueled rocket stack. The vertical actuators can even add delta-v at launch.

 

[scaesare]

I'm not thinking a cradle, that would be one arm.
I'm envisioning two independent arms that each pivot and cover a near 180 degree region extending out their length. (90 degrees to tower being ideal).
They track the booster's entry and swing into position as it passes by.
Black: tower
Blue: arms
Orange: capture area
View attachment 622895
Not really any tolerances, critcal parameters are arm manuvering speed and accuracy versus booster lateral speed.
Optionally, the fins can move to an angled downward position to grab the arms and tuck them in. Other pair should be folded for clearance.

For fun, imagine holding the rocket by all four points for launch. Can then be high off the ground, and the base never needs to support a fully fueled rocket stack. The vertical actuators can even add delta-v at launch.

Ah that makes sense. Both arms have a starting position with as wide an angle as possible and the sweep closed to hone in on the booster position.

Still, that's gonna be some pretty precise control on both the rocket and arm side.

Given what we saw with the SN8 bellyflop test, I wonder if the mass of the SH booster and the ability to cut off engines and throttle the remaining one(s) down would allow the rocket to essentially hover? Or at least make the final approach much less hot than is possible with the Falcon 9's "hover-slam". That would allow more time to position the tower arms.

 

[mongo]

Ah that makes sense. Both arms have a starting position with as wide an angle as possible and the sweep closed to hone in on the booster position.

Still, that's gonna be some pretty precise control on both the rocket and arm side.

Given what we saw with the SN8 bellyflop test, I wonder if the mass of the SH booster and the ability to cut off engines and throttle the remaining one(s) down would allow the rocket to essentially hover? Or at least make the final approach much less hot than is possible with the Falcon 9's "hover-slam". That would allow more time to position the tower arms.

The rocket can't accelerate sideways very quickly due to mass, so tracking the path should not be that hard. Can have lots of actuator force on tap. Start out far and continually close the gap as it descends.

For sure, SH with 28? engines could hover, however the dynamics are not great. Unless there is a large amount of RCS capability, the rocket needs to tilt to counter crosswinds, so the volume it could occupy while manuvering is large. Coming in on a specific trajectory with spacing from the tower and capturing as quickly as possible might be safer. With swing arms, the rocket could have a tangental path that never intersects the tower.

 

[JRP3]

What about "V" shaped catch arms? Would allow for some deviation and be self centering.

 

[mongo]

What about "V" shaped catch arms? Would allow for some deviation and be self centering.

Which way does the V go?
It could be a single arm with a V/ cradle at a right angle that captures the booster as it passes across the tower. Needs low resistance in/ out movement to avoid adding moments to the rocket.