totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

On 5/20/2021 at 11:20 AM, RealKerbal3x said:

Maybe? You do have to take into account how massive Starship is when full of propellant, though. Isn't it like 1200 tons fully loaded?

I ended up doing the math and it was no-contest at all. Inertia doesn't matter and neither does TWR; it's just a question of whether total aerodynamic drag exceeds the thrust of six engines. Drag at MaxQ wouldn't even exceed the thrust of one engine.

On 5/20/2021 at 11:46 AM, tater said:

TWR looks to be >1, but pretty low.

I was initially confused because I thought you'd need TWR>>1 to oppose drag, but drag doesn't care about the direction of gravity. The math works the same no matter what direction you're headed. As long as Superheavy's engines don't keep running, Starship has more than enough thrust to pull away regardless of drag.

It does not, however, have enough thrust to pull away rapidly enough on the pad.

21 hours ago, JoeSchmuckatelli said:

Biggest thing in the solar system, and one of the hardest to hit.

So - is it easier to use Jupiter or Venus to get your garbage tug to hit the sun ?

Just go all Matt Lowne and do a Venus-Earth-Venus gravity assist in order to get a Jupiter flyby in order to get a reverse gravity assist at Saturn to drop your periapsis into the Sun.

If you want more velocity headed into the sun then line up your Saturn reverse gravity assist with another (reverse) Venus gravity assist on your way back.

[RyanRising]

44 minutes ago, RealKerbal3x said:

The test is orbital, just because it won't go all the way around the Earth doesn't mean it's suborbital. Starship will achieve orbital velocity.

I’d say it’s “orbital-ish” at best. Usually when you’re concerned about whether or not something is in orbit, you want to know whether it’s in a stable orbit. Otherwise stuff like sounding rockets are orbital, only with very negative periapses. Since Starship in that test will not be in a stable orbit and will not have to perform a deorbit burn to achieve controlled reentry, I don’t think it’s fair to say it’s orbital without any caveats. It achieves almost orbital velocity, but not quite there, by design. 
 

Basically, if this flight is orbital, then Astra’s Rocket 3.2 flight is orbital. And I don’t think either, despite getting very close, are.

[JoeSchmuckatelli]

18 minutes ago, sevenperforce said:

If you want more velocity headed into the sun then line up your Saturn reverse gravity assist with another (reverse) Venus gravity assist on your way back.

Of course we want max velocity - how else are we going to reach the Sun's inner Alderson point with shields down?

[StrandedonEarth]

Just now, JoeSchmuckatelli said:

Of course we want max velocity - how else are we going to reach the Sun's inner Alderson point with shields down?

That’s Crazy Eddie talk. 

[JoeSchmuckatelli]

54 minutes ago, RealKerbal3x said:

The test is orbital, just because it won't go all the way around the Earth doesn't mean it's suborbital

Okay - well is that a 'technical definition' based on altitude?  Because to me, 'orbital' means 'not hitting the planet' where 'suborbital' means it gets wet or dirty at the end of the flight.

[SpaceFace545]

6 minutes ago, JoeSchmuckatelli said:

Okay - well is that a 'technical definition' based on altitude?  Because to me, 'orbital' means 'not hitting the planet' where 'suborbital' means it gets wet or dirty at the end of the flight.

that's a very interesting set of terms for something to be orbital. starship going orbital isn't actually completing a complete orbit so it would be a suborbital mission where it momentarily flies at orbital velocities.

[tater]

For the test in question what matters is entry velocity.

So it's certainly doing an orbital velocity reentry.

Functionally, that means it could have been in a stable orbit.

[sevenperforce]

12 minutes ago, RyanRising said:

I’d say it’s “orbital-ish” at best. Usually when you’re concerned about whether or not something is in orbit, you want to know whether it’s in a stable orbit. Otherwise stuff like sounding rockets are orbital, only with very negative periapses. Since Starship in that test will not be in a stable orbit and will not have to perform a deorbit burn to achieve controlled reentry, I don’t think it’s fair to say it’s orbital without any caveats. It achieves almost orbital velocity, but not quite there, by design. 

Basically, if this flight is orbital, then Astra’s Rocket 3.2 flight is orbital. And I don’t think either, despite getting very close, are.

Disagree. Astra Rocket 3.2's upper stage cut off at 7.2 km/s when it needed to be at 7.68 km/s. With an apogee of 390 km, the intended velocity would have given it a perigee of 122 km; its actual final velocity placed its perigee 1,066 km below the surface of the earth, somewhere near the bottom of the mantle.

Starship can enter an orbit with a high apogee and a perigee at around 30 km above the surface of the earth...definitely orbital speed, just eccentric enough to ensure re-entry in one orbit.

[JoeSchmuckatelli]

8 minutes ago, JoeSchmuckatelli said:

Okay - well is that a 'technical definition' based on altitude?  Because to me, 'orbital' means 'not hitting the planet' where 'suborbital' means it gets wet or dirty at the end of the flight.

 

Just now, tater said:

For the test in question what matters is entry velocity.

So it's certainly doing an orbital velocity reentry.

Functionally, that means it could have been in a stable orbit.

Best answer - makes sense to Grog.

[tater]

Just now, SpaceFace545 said:

that's a very interesting set of terms for something to be orbital. starship going orbital isn't actually completing a complete orbit so it would be a suborbital mission where it momentarily flies at orbital velocities.

It's definitely a gray area, because there is zero need for "orbital" flights that are at the very edge of stability. The only reason for such a trajectory is testing.

Anyone sensible would know that if SS did a tiny burn at apogee for that profile it would be in a stable orbit for at least some number of revolutions.

[Spaceman.Spiff]

37 minutes ago, sevenperforce said:

Just go all Matt Lowne and do a Venus-Earth-Venus gravity assist in order to get a Jupiter flyby in order to get a reverse gravity assist at Saturn to drop your periapsis into the Sun.

Ah, didn't Scott do that?

[tater]

7 minutes ago, sevenperforce said:

Starship can enter an orbit with a high apogee and a perigee at around 30 km above the surface of the earth...definitely orbital speed, just eccentric enough to ensure re-entry in one orbit.

Yeah, technically they are all orbits, but we only usually consider the ones that don't intersect the ground.

If they fly this before SLS, for sure we can expect the SLS apologists to claim it wasn't a "real orbit," even though it's the best possible choice for safety, and anyone capable of doing the math would know it could have been in a stable orbit. Shuttle could have easily taken the External Tank to LEO, for example, which everyone knew (wet labs discussed using them, or a giant Mars ship in the Kim Stanley Robinson book, Red Mars).

Edited May 21, 2021 by tater

[Spaceman.Spiff]

22 minutes ago, RyanRising said:

I’d say it’s “orbital-ish” at best. Usually when you’re concerned about whether or not something is in orbit, you want to know whether it’s in a stable orbit.

You can determine that with MATH.

By that logic, Gagarin didn't "orbit" either.

[kerbiloid]

3 minutes ago, tater said:

If they fly this before SLS, for sure we can expect the SLS apologists to claim it wasn't a "real orbit,"

It will be a highly elliptical orbit with underground perigee.

An orbit passing through the space vacuum and the iron core at once.

Edited May 21, 2021 by kerbiloid

[southernplain]

From the FCC filing:

“The Orbital Starship will continue on flying between the Florida Straits. It will achieve orbit until performing a powered, targeted landing approximately 100 kilometers (about 62 miles) off the northwest coast of Kauai in a soft ocean landing,” 

Emphasis mine.

All the rest is semantics honestly. Starship/Superheavy is capable of orbital flight whether they do so or not. Moreover, the point is not to go to orbit, it is to test flight and reentry. Also from the filing: 

"SpaceX intends to collect as much data as possible during flight to quantify entry dynamics and better understand what the vehicle experiences in a flight regime that is extremely difficult to accurately predict or replicate computationally."

Edited May 21, 2021 by southernplain

[SpaceFace545]

6 minutes ago, tater said:

even though it's the best possible choice for safety

how is starship safer than a traditional rocket, sure SLS has two massive SRBs but it at least has an LES system.

[tater]

3 minutes ago, SpaceFace545 said:

how is starship safer than a traditional rocket, sure SLS has two massive SRBs but it at least has an LES system.

How do you get "safer" from a post where all I say is that this is the safest trajectory for testing orbital EDL?

Uncrewed spacecraft don't need an LES system, so that is clearly not remotely related to what we are discussing—the orbital test flight of SN20/BN3.

[RealKerbal3x]

7 minutes ago, SpaceFace545 said:

how is starship safer than a traditional rocket, sure SLS has two massive SRBs but it at least has an LES system.

As tater said, this is kind of irrelevant to the current discussion, but I'll just quote what I posted yesterday about this.

On 5/20/2021 at 4:11 PM, RealKerbal3x said:

Starship is intended to be made safe for crew not through an abort system (which would be impractical for the large crews SpaceX eventually intend it to carry), but through being extremely reliable and fault-tolerant. As a result, crewed Starship is a long way off - it could be a thousand flights before it's trusted with a crew.

Of course, it'll probably never be as safe as modern commercial airlines for the simple fact that it's a rocket. But it might well be safe enough that you could fly on it without fearing for your life - perhaps comparable to the early days of passenger air travel.

 

[SpaceFace545]

4 minutes ago, tater said:

How do you get "safer" from a post where all I say is that this is the safest trajectory for testing orbital EDL?

Uncrewed spacecraft don't need an LES system, so that is clearly not remotely related to what we are discussing—the orbital test flight of SN20/BN3.

My bad. 

[tater]

Just now, SpaceFace545 said:

My bad. 

No worries, rapid fire back and forths get that way sometimes, particularly given the tangents we go off on, lol.

[Beccab]

I'm surprised this wasn't posted already: Flyer sent by spacex to congress,

and counterflyer sent by Blue Origin https://imgur.com/a/ahgjGG4

Edit: Oh god, spacex even put that blue origin hasn't sent a single rocket to orbit yet

Edited May 21, 2021 by Beccab

[SpaceFace545]

Haha, these two sure hate each other. I am intrigued about what Bezo’s is saying about China. What ties does China have with SpaceX?

[Beccab]

1 minute ago, SpaceFace545 said:

Haha, these two sure hate each other. I am intrigued about what Bezo’s is saying about China. What ties does China have with SpaceX?

I believe that was just a general "We are the National Team, we are better!" unless I misunderstood

[Spaceman.Spiff]

Interesting that they used the good ol China scare technique. 

[southernplain]

4 minutes ago, SpaceFace545 said:

I am intrigued about what Bezo’s is saying about China. What ties does China have with SpaceX?

Musk is friendly with China on some level so Tesla can do business there.

Regarding SpaceX though, this is just political posturing. In space policy China is a suitable boogeyman, like "we need to get to the Moon before China does."

SpaceX is saying that the amendment will slow the program due to litigation.

BO is saying that sole-sourcing from SpaceX exposes the program to possible delays if they run into problems with their technology development program.