Quote from: TheRadicalModerate on 04/02/2024 07:26 am...The lowest viable SSO is 274 x 274 x 97.7°, and you want to launch from Kodiak. So our delta-v budget is:+475m/s to cover launching against Earth's rotation, plus azimuth changes (again, spreadsheet hacking involved)...That swing from a 408m/s rotational advantage to a 475m/s disadvantage...Are you sure you're not counting the same penalty twice? What's the difference between the "launching against Earth's rotation" penalty and the "azimuth" penalty?At 57.4° latitude, Kodiak's pure eastward velocity is only 250 m/s. Solving for azimuth via cos(inclination) = cos(latitude) × sin(azimuth), the launch azimuth is 194.1°. Sine of 194.1° is -0.24, so the downrange component of that eastward velocity is only 250 m/s × -0.24 = -61 m/s.That's a far cry from -475 m/s. Why the discrepancy I wonder?
...The lowest viable SSO is 274 x 274 x 97.7°, and you want to launch from Kodiak. So our delta-v budget is:+475m/s to cover launching against Earth's rotation, plus azimuth changes (again, spreadsheet hacking involved)...That swing from a 408m/s rotational advantage to a 475m/s disadvantage...
Yow.OK, thanks for putting so much effort into making that very clear.Cheers, Martin
Right now, SpaceX is scheduled to attempt the first demonstration of a large-scale propellant transfer between two Starships in orbit next year. [Calendar 2025]
During these upcoming Starship test flights, engineers will measure the slosh of propellants inside the ship, along with tank pressures, and observe how the fluids respond to impulses from small thrusters. In microgravity, these small rocket jets provide "settling thrust" to guide the ship's liquid toward the outflow needed for refueling.
Engineers will also monitor the boil-off rates of the methane and liquid oxygen in space. Over time, cryogenic liquids transition to a gaseous state without insulation or other measures to prevent boil-off. SpaceX and NASA officials want to know how much of the propellant will be lost from boil-off to know how many refueling tankers they need to launch for a Starship lunar landing mission.
Both ships involved in the refueling demo will also have thermal insulation and vacuum jacketing around internal plumbing to limit boil-off.
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Computer models and flight data from numerous rockets show it is possible to gain control over cryogenic boil-off, tank pressures, and propellant settling in space. But no one has ever attempted to flow cryogenic propellants from one spacecraft to another in orbit."In my mind, all the technical issues associated with cryo transfer in space are solved," said George Sowers, former chief scientist at SpaceX rival United Launch Alliance and a longtime proponent of depoting propellants in space. "It’s just a matter of demonstrating it and fine-tuning the technology and the procedures. So, I think we’re on the cusp. I’m happy to see SpaceX taking the steps to make it work.
Once the two Starships come together, they will connect using the same ports SpaceX uses to load propellants on the launch pad. Then, SpaceX will fine-tune tank pressures and fire propellant settling thrusters. "At that point, they'll open up and let the propellant flow."The propellants will flow from one vehicle to the other using a pressure differential, or "delta," between the donor tank and the recipient tank. This is a simpler solution than relying on pumps."The fundamental flow mechanism is because of the pressure delta across the umbilical," Kshatriya said.
The results of this refueling demonstration will allow SpaceX and NASA engineers to calculate how many refueling tankers they will need to fill up a Starship heading for the Moon. SpaceX's current estimate is approximately 10 refueling launches for one Artemis landing mission, but there are error bars on each side of this number.
Everyone was pretty sure they'd use ullage engines, but this is the first time I've seen that confirmed.
QuoteBoth ships involved in the refueling demo will also have thermal insulation and vacuum jacketing around internal plumbing to limit boil-off.So neither will be a "vanilla" Starship--whatever that means. :-)
Would someone please help?Afaik, a simple sunshade would allow all of any depot to radiate to outer space at near 0 degrees K.Where is the heat to be managed coming from?
This is a nit, but let's avoid the term "ullage engines".
"Internal plumbing" isn't the same as full tankage insulation. It may make sense just to make all the QD connections insulated for all cases and have done with it. Even a vanilla Starship will need to receive prop from a depot. The problem is that a substantial amount of prop will be boiled off as the transfer plumbing chills down. If you can maintain that plumbing in a nominally cold state, it'll reduce losses by quite a bit.On the other hand, a Starlink / pez-dispenser Starship won't ever receive prop. That might be the special case.
Both Earth and the Moon are substantial re-radiators of heat from the Sun. India’s first Lunar orbiter was, IIRC, damaged by heat from the Moon on daylight passes. As well as protecting from the Sun there will need to be protection from other parts of the spacecraft operating environment.
Quote from: TheRadicalModerate on 05/04/2024 09:02 pmThis is a nit, but let's avoid the term "ullage engines". Fair enough. I'd still like to know what kind of settling engines they're going to use. If it's cold gas, they may end up using up a significant fraction of the propellants.
It is only needed during the actual transfer. Also, there will be a lot of gas generated during the transfer ops.
QuoteThe two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.Again, no surprise, but nice to see confirmation.
Quote from: Greg Hullender on 05/04/2024 06:09 pmQuoteThe two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.Again, no surprise, but nice to see confirmation.The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.
Quote from: Thrustpuzzle on 05/06/2024 04:47 amQuote from: Greg Hullender on 05/04/2024 06:09 pmQuoteThe two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.Again, no surprise, but nice to see confirmation.The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.Dorsal or ventral?
Quote from: tyrred on 05/06/2024 06:51 amQuote from: Thrustpuzzle on 05/06/2024 04:47 amQuote from: Greg Hullender on 05/04/2024 06:09 pmQuoteThe two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.Again, no surprise, but nice to see confirmation.The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.Dorsal or ventral?Dorsal = back. Ventral = belly.
Quote from: Twark_Main on 05/06/2024 08:47 amQuote from: tyrred on 05/06/2024 06:51 amQuote from: Thrustpuzzle on 05/06/2024 04:47 amQuote from: Greg Hullender on 05/04/2024 06:09 pmQuoteThe two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.Again, no surprise, but nice to see confirmation.The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.Dorsal or ventral?Dorsal = back. Ventral = belly.Yes, belly to belly is wrong but it is also better at describing the concept to a layman than back to back which is ambiguous in English (likely due to human bipedalism).
My apologies for the non-technical reference, but all the back-to-back and belly-to-belly talk is begging for this soundtrack.[snip]The old timers may appreciate the reference and the younger crowd will benefit from learning it