Jump to content

Could the SuperHeavy booster be SSTO?


Recommended Posts

Posted (edited)

 Starship will use 30 tons of propellant as ballast in the nose on landing to help maintain stability:

 Note this will only be used on landing so would not be included for accounting of the mass as an expendable stage. The nose cone and nose cone barrel weighs ~17 tons. SpaceX will also save about ~7 tons off the tank mass on shaving down the tank thickness from 4mm to 3 mm. That's 54 tons off the 120 tons often cited for the Starship "dry mass", bringing it down to 66 tons. The attempt here is to estimate the dry mass as an expendable stage. But there's still the mass of the TPS, landing legs, and flaps.

 For the landing legs we can estimate that as following the Falcon 9 booster model of ~10% of the stage dry mass, so ~12 tons for the legs on Starship, when SpaceX is going by 120 tons as the dry mass. So we're now down to ~54 tons as an expendable dry mass. And the TPS? On the NasaSpaceflight.com forum that has been estimated as from 5 to 10 tons. So the expendable dry mass might be down to 44 tons. Then there is still the mass of the flaps that needs to be subtracted off for the expendable dry mass. Quite conceivable then that the expendable dry mass might be less than 40 tons.

 This is important to know because this is the form of the stage that would be used as the lunar lander, as SpaceX is intending it to be expendable in their lunar plan. Note also the payload section would also be removed in this configuration, with the lunar crew module being directed attached to the tank section via an adapter.

 Elon acknowledge this configuration would be much lighter and would therefore take fewer refuelings:

 If the Starship expendable without payload section or reusability systems would only mass ~40 tons then that needs to be acknowledged by SpaceX if that means the launches that needs to be paid for the U.S. taxpayers could be cut from ~16 to ~4.

 See discussion here:

https://exoscientist.blogspot.com/2022/09/the-nature-of-true-dry-mass-of-starship.html

 

  Robert Clark 

Edited by Exoscientist
Link to comment
Share on other sites

1 hour ago, Exoscientist said:

 If the Starship expendable without payload section or reusability systems would only mass ~40 tons then that needs to be acknowledged by SpaceX if that means the launches that needs to be paid for the U.S. taxpayers could be cut from ~16 to ~4.

HLS is a fixed price contract. Doesn't matter if it takes them 100 flights, NASA is paying for a demo landing, and a human landing.

Link to comment
Share on other sites

3 hours ago, Exoscientist said:

Starship will use 30 tons of propellant as ballast in the nose on landing to help maintain stability:

<snip>

 Note this will only be used on landing so would not be included for accounting of the mass as an expendable stage. The nose cone and nose cone barrel weighs ~17 tons. SpaceX will also save about ~7 tons off the tank mass on shaving down the tank thickness from 4mm to 3 mm. That's 54 tons off the 120 tons often cited for the Starship "dry mass", bringing it down to 66 tons. The attempt here is to estimate the dry mass as an expendable stage. But there's still the mass of the TPS, landing legs, and flaps.

 For the landing legs we can estimate that as following the Falcon 9 booster model of ~10% of the stage dry mass, so ~12 tons for the legs on Starship, when SpaceX is going by 120 tons as the dry mass. So we're now down to ~54 tons as an expendable dry mass. And the TPS? On the NasaSpaceflight.com forum that has been estimated as from 5 to 10 tons. So the expendable dry mass might be down to 44 tons. Then there is still the mass of the flaps that needs to be subtracted off for the expendable dry mass. Quite conceivable then that the expendable dry mass might be less than 40 tons.

Why are you doing all these random estimates and guesstimates when Elon has already said how much an expendable Starship would mass?

40 tonnes dry, 1200 kg of propellants.

As an SSTO, though, you'd need to add six more engines, so tack on 10 tonnes more. So 50 tonnes dry.

~16 vs ~4 is a totally different question than anything related to SSTO applications, so that's immaterial.

Link to comment
Share on other sites

22 hours ago, tater said:

HLS is a fixed price contract. Doesn't matter if it takes them 100 flights, NASA is paying for a demo landing, and a human landing.

 The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander.  Then that contract price should have been less.

  Robert Clark

Link to comment
Share on other sites

6 minutes ago, Exoscientist said:

 The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander.  Then that contract price should have been less.

Why? Why would SpaceX leave money on the table? They were already 1/3-1/2 the price of the competing bids for vastly more capability.

If they do it with fewer launches, they make more money.

Seriously, this is like asking why we don't just pay what we SHOULD be paying for SLS. There's zero reason for SLS to be $3B-$4B per launch, should be a few hundred million. Why doesn't Boeing/LockMart/NG/et al just charge us 10X less, there's no way it actually costs ~$100M per RS-25, after all, when we know similar engines are orders of magnitude cheaper (Be-4 ~$7M per, Raptor ~$1M).

Link to comment
Share on other sites

Posted (edited)
On 10/6/2022 at 4:45 PM, sevenperforce said:

Why are you doing all these random estimates and guesstimates when Elon has already said how much an expendable Starship would mass?

40 tonnes dry, 1200 kg of propellants.

As an SSTO, though, you'd need to add six more engines, so tack on 10 tonnes more. So 50 tonnes dry.

~16 vs ~4 is a totally different question than anything related to SSTO applications, so that's immaterial.

 

 Actually, the mass of the Starship as an expendable is the entire point of the matter.  From that you see you can get quite high payload as an expendable rocket. In fact, it’s in the same percentage of gross mass range of other currently in use expendable rockets.

 About the SpaceX lunar plan, it is an extremely important thing to know if NASA, and the U.S. tax payers, are getting jobbed if the original ~$3 billion price was based on ~16 flights per mission when it will only take ~4 launches per mission.

   Robert Clark

Edited by Exoscientist
Typo
Link to comment
Share on other sites

41 minutes ago, Exoscientist said:

The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander.

Well we could also suppose that rockets are powered by unicorn farts, but that wouldn't be any closer to reality than whatever this is. ~16 were most certainly not built into the contract from the beginning. The "~16 launches" bit was part of an attack ad from Blue Origin. Rather, as Elon points out in the tweet you quote, the total tank capacity of Starship is 1200 tonnes, so with 150 tonnes of propellant delivered per fully-reusable launch, that's a max of 8 launches.

Elon further notes that they may be able to lighten the lander vehicle enough that it could make the trip to the moon on as little as half a tank, necessitating fewer prop launches. However, these would still be fully-reusable launches. NONE of this has anything to do with Starship tankers flying expendable.

But even if it did, it still wouldn't be a reason to suggest that there was something amiss about the contract price. NASA is paying for a service, not a series of launches. If SpaceX decides to reconfigure its launch system to include expendable tankers in order to do the whole thing in fewer launches, that's up to them to pay for (or reap the benefits of); NASA doesn't care. NASA only cares about the whole system meeting certain safety requirements.

26 minutes ago, Exoscientist said:

Actually, the mass of the Starship as an expendable is the entire point of the matter.

Which is why it's so puzzling that you keep trying to estimate the mass of an expendable Starship, when Elon already stated it.

26 minutes ago, Exoscientist said:

From that you see you can get quite high payload as an expendable rocket.

By this I suppose you mean an SSTO expendable Starship. If that's the case, then no, not so much once you add sea level engines. And SpaceX doesn't want to operationally throw away engines.

26 minutes ago, Exoscientist said:

In fact, it’s in the same percentage of gross mass range of other currently in use expendable rockets.

Gross mass is all well and good, but the bottom line is money.

SpaceX wants to deliver a certain amount of payload (usually propellant) to orbit. They will endeavor to do so at the lowest possible cost. Throwing away engines to save on propellant only makes sense if propellant is very expensive or upper-stage recovery is too long a pole.

30 minutes ago, Exoscientist said:

it is an extremely important thing to know if NASA, the U.S. tax payers, are getting jobbed if the original ~$3 billion price was based on ~16 flights per mission

It was not, and even if it had been, that wouldn't be meaningful. If SpaceX can do it cheaper than expected, more power to them.

Link to comment
Share on other sites

4 hours ago, sevenperforce said:

Well we could also suppose that rockets are powered by unicorn farts, but that wouldn't be any closer to reality than whatever this is. ~16 were most certainly not built into the contract from the beginning. The "~16 launches" bit was part of an attack ad from Blue Origin. Rather, as Elon points out in the tweet you quote, the total tank capacity of Starship is 1200 tonnes, so with 150 tonnes of propellant delivered per fully-reusable launch, that's a max of 8 launches.

 

 

 Actually, it was. And SpaceX went so far as detailing how long they expected it would take to make these total 16 launches per mission:

SpaceX CEO Elon Musk details orbital refueling plans for Starship Moon lander. By Eric Ralph Posted on August 12, 2021
First, SpaceX will launch a custom variant of Starship that was redacted in the GAO decision document but confirmed by NASA to be a propellant storage (or depot) ship last year. Second, after the depot Starship is in a stable orbit, SpaceX’s NASA HLS proposal reportedly states that the company would begin a series of 14 tanker launches spread over almost six months – each of which would dock with the depot and gradually fill its tanks.

In response to GAO revealing that SpaceX proposed as many as 16 launches – including 14 refuelings – spaced ~12 days apart for every Starship Moon lander mission, Musk says that a need for “16 flights is extremely unlikely.” Instead, assuming each Starship tanker is able to deliver a full 150 tons of payload (propellant) into orbit after a few years of design maturation, Musk believes that it’s unlikely to take more than eight tanker launches to refuel the depot ship – or a total of ten launches including the depot and lander.
https://www.teslarati.com/spacex-elon-musk-starship-orbital-refueling-details/

Blue Origin didn’t raise this objection arbitrarily about the number of launches. It’s because it was in the actual proposal SpaceX made to NASA, and on which SpaceX based their charge to NASA for their mission plan.
 If they now claim the number of refueling launches will only be 4, then they should amend the amount they are charging NASA for their plan.
 
  Robert Clark

 

Link to comment
Share on other sites

2 hours ago, Exoscientist said:

Blue Origin didn’t raise this objection arbitrarily about the number of launches. It’s because it was in the actual proposal SpaceX made to NASA, and on which SpaceX based their charge to NASA for their mission plan.

 If they now claim the number of refueling launches will only be 4, then they should amend the amount they are charging NASA for their plan.
 
  Robert Clark

 

That is sort of like claiming that the airline owes you money because they caught a tail-wind during your flight and used less fuel than expected.

You bought a ticket to fly from point A to point B, and so long as you get to point B in a timely fashion, you got what you paid for and do not get a refund if they happened to save money in one way or another.

Same with NASA purchasing a certain number of fights to the moon(one unmanned and one manned I think?), so long as the ships fly as expected, if SpaceX can save money by adding unicorn farts to the fuel mix, then why would NASA care? 

Link to comment
Share on other sites

On 9/20/2022 at 8:06 PM, tater said:

It's reused—in space.

LSS can fly RT from LEO to the lunar surface and back to LEO (propulsively) if slightly stretched, or if a tug gives it a push.

As I understand lunar starship is not designed to return to LEO, it will stay in orbit around the moon, it can be refueled and reused for additional landings however. 
I rater say lunar starship might well be lighter. With an crew of 4, even if they expand this to 7-8 it will not need the 5-6 deck crew compartments of a full manned starship. I say the cargo bay with two air locks the cargo bay can probably be pressurized, they might have one lab deck and one living space deck. then the curved nose for storage. it will still be very roomy compared to IIS.
Some chance the crew nose will be aluminium and / or composites as it reduce secondary radiation who is an weakness of steel and lighter. 
The tanker refueling LSS will either return and land as its designed to do that or be disposed. Might also be an experimental landing testing higher speed reentry. 

You could use LSS as an lunar space station then not landed. 

Link to comment
Share on other sites

2 minutes ago, magnemoe said:

As I understand lunar starship is not designed to return to LEO, it will stay in orbit around the moon, it can be refueled and reused for additional landings however. 
I rater say lunar starship might well be lighter. With an crew of 4, even if they expand this to 7-8 it will not need the 5-6 deck crew compartments of a full manned starship. I say the cargo bay with two air locks the cargo bay can probably be pressurized, they might have one lab deck and one living space deck. then the curved nose for storage. it will still be very roomy compared to IIS.
Some chance the crew nose will be aluminium and / or composites as it reduce secondary radiation who is an weakness of steel and lighter. 
The tanker refueling LSS will either return and land as its designed to do that or be disposed. Might also be an experimental landing testing higher speed reentry. 

You could use LSS as an lunar space station then not landed. 

Either architecture is possible, the props need to be in lunar orbit one way or another.

Link to comment
Share on other sites

23 hours ago, Exoscientist said:

 The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander.  Then that contract price should have been less.

  Robert Clark

16 launches who is likely more than is needed let you reuse the upper stages. Also even if payload is only 100 ton for the tanker it will not be 400 ton for an disposable tanker, perhaps 200 ton. 

Link to comment
Share on other sites

29 minutes ago, tater said:

Either architecture is possible, the props need to be in lunar orbit one way or another.

Yes but the tankers will be designed to reentry and land, or if disposable is much cheaper than LSS who can not aerobrake.9 

Link to comment
Share on other sites

6 minutes ago, magnemoe said:

Yes but the tankers will be designed to reentry and land, or if disposable is much cheaper than LSS who can not aerobrake.9 

There are a number of reasons returning LSS propulsively to LEO is preferable.

1. You could load new crew, obviating SLS/Orion.

2. LSS also has non-propellant consumables, plus cargo as delivered mass to the surface. Those have to be loaded on LSS someplace.

Link to comment
Share on other sites

8 minutes ago, tater said:

There are a number of reasons returning LSS propulsively to LEO is preferable.

1. You could load new crew, obviating SLS/Orion.

2. LSS also has non-propellant consumables, plus cargo as delivered mass to the surface. Those have to be loaded on LSS someplace.

Yes but orion is kind of an requirement as I understand. You could use an cargo dragon for resupply if launched on FH, spaceX plan an disposable dragon cargo version for the moon anyway. Or perhaps have an cargo compartment on the refueling tanker SS. using engines to brake LSS into LEO will be expensive. 
Dragon 2 to Moon on FH, qualifying manned SS to aerobrake into LEO, crew get into leo and back on dragon 2 is another option. 
 

Link to comment
Share on other sites

32 minutes ago, magnemoe said:

Yes but orion is kind of an requirement as I understand. You could use an cargo dragon for resupply if launched on FH, spaceX plan an disposable dragon cargo version for the moon anyway. Or perhaps have an cargo compartment on the refueling tanker SS. using engines to brake LSS into LEO will be expensive. 
Dragon 2 to Moon on FH, qualifying manned SS to aerobrake into LEO, crew get into leo and back on dragon 2 is another option. 
 

Resupply of LSS in LLO with Dragon, or DragonXL means multiple trips, multiple Dragons/DragonXLs thrown away.

I outlined the propulsive dv budget either up this thread, or in another one. It's not a big deal.

The Depot vehicle can fill the LSS in LEO, then follow it to LLO. It can either refill for another landing sortie, then fly back to LEO propulsively, or it could refill LSS, then BOTH vehicles fly back to LEO propulsively.

I see no reason why returning LSS to LEO is not preferable.

Link to comment
Share on other sites

  • 4 weeks later...

 

 It looked like the Air Force buzzed the Starbase with their most advanced fighter:

 

 Actually, they were just practicing for a nearby air demonstration. But this is rather ironic because I advise rather than using 30 tons of ballast to maintain CG ahead of CP position for stability, thus subtracting that amount from payload, use computerized control to maintain stability as commonly used on fighter jets. This is taken to an extreme level with the F-22 with its large control surfaces at the rear of the plane:

 

 The flaps on the Starship could serve the same function. Instead of just letting them fold upwards to various degrees against the sides of the rocket, allow them also to rotate forwards and backwards as done with the F-22.

 

  Robert Clark

Link to comment
Share on other sites

1 hour ago, Exoscientist said:

But this is rather ironic because I advise rather than using 30 tons of ballast

Starship's ballast is also its landing propellant. If you remove that, there's no way to recover the stage short of completely re-engineering it into some sort of spaceplane.

1 hour ago, Exoscientist said:

use computerized control to maintain stability as commonly used on fighter jets.

This is already what they do. The flaps aren't just there for decoration, they move to control the vehicle using differential drag, and can be used to trim it for different return payload masses.

In fact, Starship probably isn't passively stable at all, so computer control is essential.

1 hour ago, Exoscientist said:

This is taken to an extreme level with the F-22 with its large control surfaces at the rear of the plane:

The flaps on the Starship could serve the same function. Instead of just letting them fold upwards to various degrees against the sides of the rocket, allow them also to rotate forwards and backwards as done with the F-22.

Now I'm no expert on aerodynamics, but this doesn't seem like it would be much of a benefit to control authority given the high-AoA re-entry profile of Starship. The F-22's all-moving control surfaces contribute decent lift, compared to Starship's which are mostly there to increase drag.

Also, seeing as they've already had trouble with thermal protection around the flaps, this also sounds like an absolute nightmare to protect from re-entry.

Edited by RealKerbal3x
fixed quotes
Link to comment
Share on other sites

54 minutes ago, Exoscientist said:

The flaps on the Starship could serve the same function. Instead of just letting them fold upwards to various degrees against the sides of the rocket, allow them also to rotate forwards and backwards as done with the F-22.

Apart from the extraordinary weight penalty of having flaps and hinges which move in multiple axes rather than just one, adding another axis of control authority to the aft flaps won't help at all if the  moment arm from the center of mass isn't long enough. That's just basis physics.

Locating the landing propellant in the nose rather than keeping it in the LOX tank pulls the center of mass just far forward enough that the aft flaps have control authority. Without this, the aft flaps would have zero control authority, because the engines are very heavy and so the center of mass would be between the flaps themselves. Giving the aft flaps a new control axis wouldn't help because zero times anything is still zero.

Link to comment
Share on other sites

On 11/5/2022 at 12:08 PM, RealKerbal3x said:

This is already what they do. The flaps aren't just there for decoration, they move to control the vehicle using differential drag, and can be used to trim it for different return payload masses.

In fact, Starship probably isn't passively stable at all, so computer control is essential.

 I’m suggesting they should do more than just fold up against the sides to varying degrees. They should also rotate forward and backwards. This would provide better control of the pitching moment.

 The Chinese 5th-generation fighter J-20 is another example with extreme rotatable control surfaces:

https://www.reddit.com/r/aviation/comments/ynb0am/chinese_j20_fighter/?utm_source=share&utm_medium=ios_app&utm_name=iossmf

The 30 ton propellant kept on reserve for landing is far more than needed for the landing burn. The landing burn might require only ~250 m/s delta V when you consider the low terminal velocity of ~90 m/s plus gravity drag:

Belly-Flop-MAIN-Reshoot.00_31_14_17.Stil
 

 This would require a small amount of propellant to be burned considering the Raptor has  330s sea level Isp.  And Elon has acknowledged the 30 tons ballast in the nose is to help stability.

   Robert Clark

Link to comment
Share on other sites

The 30t of propellant is needed for landing. Putting it in the nose for stability is a two birds one stone situation. Getting rid of the landing propellant results in a crater regardless of the aerodynamic stability.

Two-axis hinges are heavy, mechanically complex, difficult to defend against plasma penetration, and unnecessary because single-axis is sufficient.

Edited by RCgothic
Link to comment
Share on other sites

11 hours ago, RCgothic said:

The 30t of propellant is needed for landing. Putting it in the nose for stability is a two birds one stone situation. Getting rid of the landing propellant results in a crater regardless of the aerodynamic stability.

Two-axis hinges are heavy, mechanically complex, difficult to defend against plasma penetration, and unnecessary because single-axis is sufficient.

This. All of it.

Link to comment
Share on other sites

On 11/7/2022 at 4:26 AM, RCgothic said:

The 30t of propellant is needed for landing. Putting it in the nose for stability is a two birds one stone situation. Getting rid of the landing propellant results in a crater regardless of the aerodynamic stability.

Two-axis hinges are heavy, mechanically complex, difficult to defend against plasma penetration, and unnecessary because single-axis is sufficient.

 If you do the calculation the amount of propellant used for landing is far less than 30 tons. 

   Robert Clark

Link to comment
Share on other sites

6 hours ago, Exoscientist said:

 If you do the calculation the amount of propellant used for landing is far less than 30 tons. 

   Robert Clark

Still need sufficient props in the lines to prevent the turbos sucking vapors and Rudding. I’ll bet it’s not an insignificant amount. Plus reserves, of course. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...