About the Tesla Roadster going to 'Mars orbit'. The consensus seems to be now that we assume that the Roadster will not go to a Mars orbit, but only do a flyby of Mars and stay in a solar orbit with aphelion at Mars's orbit and perihelion at Earth's orbit. However, I didn't read any convincing reason for this assumption. As a matter of fact, this assumption does contradict the original tweet of Elon saying that the Roadster will go to Mars orbit, nothing else.
Why do we all assume that a ballistic capture to a high altitude Mars is not the case? ( https://en.wikipedia.org/wiki/Ballistic_capture ) Is this not possible with the low attitude control of the Tesla Roadster? Why not? It doesn't require any deep space insertion burn which the second stage can't execute. I can agree that it is a challenging task to do the Earth escape burn so accurate that the trajectory will lead to a ballistic Mars capture. But they can at least try it? I can't understand arguments I read that this is unrealistic because the spacecraft will not be sterilized, as a ballistic trajectory leads to a high altitude orbit with no chance of deorbiting any time soon. (An inaccurate Earth escape burn might lead to a 'contaminating' crash at Mars, but this risk is still valid when just a flyby is attempted)
Sorry for long post, I hope someone can give me some more information why a ballistic capture is realistic or why not.
So I decided to contact Musk. He got back to me, and gave me the info.
No, it’s not going to Mars. It’s going near Mars. He said it’ll be placed in “a precessing Earth-Mars elliptical orbit around the sun.” What he means by this is what’s sometimes called a Hohmann transfer orbit, an orbit around the Sun that takes it as close to the Sun as Earth and as far out as Mars. This is a low-energy orbit; that is, it takes the least amount of energy to put something in this orbit from Earth. That makes sense for a first flight.
So that answers why we assume no ballistic capture.
this risk [of crashing] is still valid when just a flyby is attempted
Not if you're aiming so far away from Mars that even calling it a flyby is a stretch. It'll be interesting to see the expected closest approach distance (both this year and later years). The phrase "going near Mars" in the article above is Phil Plait's editorialization, and it may be generous.
To get past planetary protection (which Elon says they complied with), all of this had to be reckoned with.
Thanks for that, I completely missed that article.
This way, could they give the second stage a bit more energy, so that the second stage can cut off a bit earlier, which means that there is some fuel left for testing a controlled re-entry of that second stage?
Too bad there is an abort! Some speculation of the cause:
After main (liquid fueled) engine ignition the computers calculate the generated thrust. They do this either by measuring the force on the hold-down clamps or by measuring the combustion chamber pressure (or both?).
When it is found that the engine thrust is too low, they decide to not let go of the hold-down clamps and shut down the liquid engine. This is all before the solid booster ignition, as they obviously cannot be stopped once fired.
A reason for the too low thrust can be too high propellant temperature. If this temperature is high, the density decreases. As the turbo pump works at a certain volume rate, this means that less mass of propellant is pumped to the engine for decreased propellant density. This could lead to not enough thrust. (Not relevant for Ariane, see below)
As said: this is all speculation. Maybe something completely different is the cause. SpaceX's Falcon 9 had an abort last year which looked very similar, I think that abort was caused by what I just speculated.
reason for the too low thrust can be too high propellant temperature.
AFAIK Ariane uses fuel and oxidizer at boiling temperatures, so they can't warm up higher than that. For F9 with sub-chilled LOX this is a problem, yes.
Good point! I forgot about this difference between those launch vehicles. Ariane doesn't use 'superchilled' propellants like Falcon 9.
I'll strike it in my post.
I will post the answer soon, but I'm pretty sure you guys will find it!
That sounds like a good idea to me. However, I do appreciate this bot in typical cases. It saves me several clicks and loading times a day.
Meme's are not allowed on /r/spacex, even the creation of meme's is banned here. Take that meme stuff to the kid pool where everything belongs. Only peer reviewed articles done by dual PHD's from Harvard's school of Philosophy are allowed here.
Watch out, you're creating a meme.
Why is that more useful than ground-based detection?
I don't think Putin would agree if the US tried to place a detector in Siberia.
The test-ban-treaty was a godsend for geologists, because the technology you use for detecting nuclear detonations is basically the same as for detecting earthquakes, and so there are detectors all over the globe.
You can't blow up a nuclear bomb in secret. And if you somehow got it buried deep enough that it wasn't detectable by earth-based sensors (which probably is not possible), you definitely aren't going to notice it from space.
The detectors on the GPS sats are aiming for atmospheric nuclear detonations. I'm not sure if these are also that detectable with seismographic sensors?
Here an example of what in orbit detectors can cause: https://en.m.wikipedia.org/wiki/Vela_Incident For me, that's a very intriguing article.
SpaceX has always said that government missions on Falcon 9 are around $90 million. GPS III satellites are pretty light at 3,880 kg, and don't require vertical integration as far as I know.
I'm pretty sure GPS-sats don't need vertical integration. It's basically 'just' a signal transmitter with a really accurate clock.
DoD-sats that require vertical integration are probably (as they're classified) very sensitive optical divices (lenses, mirrors...?), which must be taken more care of. Hence the vertical integration, which basically means that the sat can only take loads in one dimension/direction.
They are owned by SpaceX, made mostly by the company I work for (www.orbitalsystems.com). They use several types of antennae, mostly 3m and 3.7m sized units, but they just ordered our second production 5m system.
These are located all over the place, the cape, vandy, africa, new england, bermuda. We're working on 2 additional systems for the cape to support falcon heavy right now, the'll be outside for testing at the factory next week-ish.
Thanks, that's some interesting information!
What's the main benefit of taking the 5m ones instead of the current smaller size antennae? Is it also a useful upgrade for LEO communications, or is this another signal (haha signal, get it?) that SpaceX is really focusing on deep(er) space?
A Bigger dish means more gain, so you can track things farther away or things with lower power transmitters. Or keep everything the same and use a higher bandwidth (if FCC approves) and get a higher data rate.
Aha, thanks again for your reply. So I understand the bigger dish does not really point to specific applications. It just has better overall performance.
Thanks for the analysis. I like the method just as much as the results.
My question: I understand the calculations done in MATLAB, but how did you do the tracking of the top and bottom of the stage? Do you also do this in MATLAB with some kind of image recognition tool?
What happens to the second stage for deep space launches? Is it still able to deorbit or does it also end up in deep space?
My guess would be that in most cases the 2nd stage will leave the Earth's SOI. This means that it will enter an orbit around the sun which will last about forever (for any reasonable time frame).
I really like this kind of graphs, thanks for creating them! A few questions arise for me after seeing those. But be aware, I'm just an amateur so please correct me if I'm wrong!
From the first graph you can see that the CRS missions are throttling down at MaxQ to decrease stresses on the rocket at that point. This means a little loss of overall performance of the rocket. This is affordable due to the relatively low destination orbit of the CRS missions. Question: Would a significant payload mass increase be possible for the Dragon, if the rocket didn't throttle down like the other missions?
It looks like the last mission (Iridium) has the best performance. The acceleration and velocity are highest at any point in time. However, if I recall correctly, the payload mass of this mission was the highest. How is this possible? Did SpaceX find a way to get some more power out of this F9FT?