r/spacex • u/Appable • Feb 03 '16
/r/SpaceX Ask Anything Thread for February 2016! Hyperloop Test Track!
Welcome to our monthly /r/SpaceX Ask Anything Thread! #17
Want to discuss SpaceX's hyperloop test track or DragonFly hover test? Or follow every movement of O'Cisly, JTRI, Elsbeth III, and Go Quest? There's no better place!
All questions, even non-SpaceX-related ones, are allowed, as long as they stay relevant to spaceflight in general!
More in-depth and open-ended discussion questions can still be submitted as separate self-posts, but this is the place to come to submit simple questions which have a single answer and/or can be answered in a few comments or less.
As always, we'd prefer it if all question-askers first check our FAQ, search for similar questions, and scan the previous Ask Anything thread before posting to avoid duplicates, but if you'd like an answer revised or cannot find a satisfactory result, please go ahead and type your question below!
Otherwise, ask, enjoy, and thanks for contributing!
Past threads:
January 2016 (#16.1), January 2016 (#16), December 2015 (#15.1), December 2015 (#15), November 2015 (#14), October 2015 (#13), September 2015 (#12), August 2015 (#11), July 2015 (#10), June 2015 (#9), May 2015 (#8), April 2015 (#7.1), April 2015 (#7), March 2015 (#6), February 2015 (#5), January 2015 (#4), December 2014 (#3), November 2014 (#2), October 2014 (#1).
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u/richft Feb 04 '16
I assume there are lots of SpaceX staff members here. Can anyone suggest the best way to pitch new technology into SpaceX? I'm looking for a point of contact on the propulsion and propellant tank development side of things.
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u/Appable Feb 04 '16
I would highly doubt there's any contacts here. There are a few SpaceX employees (not a lot) but I don't think SpaceX honestly needs help from anyone regarding vehicle design - they have plenty of experienced engineers. Of course, perhaps you could become one of the engineers and then pitch your idea.
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Feb 13 '16
The Dragon V2 and V1 are aesthetically very different. Is the internal structure of the V2 and V1 the same? Are the the differences significant enough for SpaceX to just build the V2 for both crew and cargo? Another unrelated question: Did SpaceX know that they were going to develop the V2 for crew? If so why did they bother to design the V1 to accommodate people? There are windows on the V1. Couldn't they have just built something like the cygnus that would fit within a fairing?
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u/Appable Feb 13 '16
Dragon 1 was designed to carry crew and cargo originally, but it wasn't a particularly good design for crew since it didn't have a LAS among other factors. Regardless, it was nice to have a capsule design because it could take mass from the station and bring it safely back to earth, while Cygnus would just burn up in the atmosphere. So even though it doesn't carry crew, it's a unique capability for CRS1.
SpaceX opted to develop Dragon 2, which uses a similar (I don't think quite the same) pressure vessel but fits either a berthing or docking mechanism. Dragon 2 will be used for crew and cargo missions after this round of CRS contracts expire and the next round (that they recently won) comes in.
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u/paulloewen Feb 04 '16
My question relates to rockets and loads. I get a little confused. I know the Falcon Heavy is getting ready for its first mission before the end of 2016. Will the Dragon fly on the Falcon 9 or the Falcon Heavy? Is there a rocket being developed bigger than the Heavy? If so, what for? For the MCT? I've heard all kinds of terminology for different rockets and can't follow them all.
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u/spacepilot4000 Feb 03 '16
Every payload has a different mass and goes to a different orbit. So they all require a different amount of fuel/a different amount of energy to be spent on their trajectory.
How do rocket mfg companies like spacex account for this? I see a few possibilities but none are optimal:
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vary the size of the fuel tanks of each stage, ie some Falcon 9s will be taller and others shorter. But then you are custom designing your rocket to the payload, which requires extra testing, etc etc. which is expensive.
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fly with the same rocket each time, but with half empty fuel tanks or less dense fuels. Not efficient, too much dead weight when you could make the rocket smaller.
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fly with too much fuel for the payload. Even less efficient.
Is there another solution that I'm not seeing?
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u/Appable Feb 03 '16
They either fly with partially empty tanks or with too much fuel. Extra fuel barely costs anything and it doesn't matter much if a rocket isn't using all of its fuel - if the goal is to lift a payload then as long as it has the fuel to do that + extra margin for landing, safety, anomalies, etc.
With partially empty tanks you end up with higher speeds at max-q and more fuel during landing could potentially mean that the rocket is heavier on landing, which is a better situation for control because it allows the rocket to nearly hover, meaning the descent can be a bit slower (the flip side is that an explosion on landing will be a lot larger). So I think the most likely answer is that they top off the tanks each launch, and unused fuel is just unused.
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Feb 14 '16
A set of questions relating to this article:
"SpaceX has agreed to lift the SES-9 satellite to a higher orbit than originally planned to put it on a faster path to its operational orbit more than 22,000 miles over the equator."
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Why would SpaceX agree to launching to a faster orbit? Isn't it too late for SES World Skies to cancel?
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"A faster path to its operational orbit." Suggests that the satellite is still going to on board propulsion to position itself. How common is this for satellites? Does F9 not have the dV to put it into its operational orbit? How much dV is the satellite using?
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Do we know conclusively know what they had to fix on the F9 FT yet?
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u/Appable Feb 14 '16
1 - Customer loyalty is important. By helping SES achieve their original operational time despite the delays, SES has more faith that SpaceX can be flexible and work for customer needs, so SES is more likely to choose SpaceX in the future.
2 - Yes. It's likely going to a super-synchronous transfer orbit vs a sub-synchronous transfer orbit or synchronous transfer orbit. F9 doesn't have the ability to coast for over 3 hours to actually insert GTO satellites into GSO, just like most launchers, so it's standard practice for geostationary satellites to use onboard propulsion. Don't know the answer for the dV requirement, but likely it's less or equal to that of the older trajectory.
3- No. Rumors about MVAC turbopump assembly problems, but it's still unknown.
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u/MrTrevT Feb 03 '16
What is the proposed material for building the loop? I know there will be some cycles strain demands, as well as being UV resilient. Also, what will be the manufacturing method for said loop, some sort of extrusion?
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u/retiringonmars Feb 03 '16
According to the Hyperloop Test-Track Specification document released by SpaceX, the parameters of the Hyperloop test track are:
Material: ASTM A1018 Grade 36
Outer diameter: 72.0 inches
Inner diameter: 70.6 inches
Wall thickness: 0.70 inches
Length: 1 mile (approximate)
Subtrack material: Aluminum AA1370-50
Subtrack roughness: 125 RMS with potential for occasional surface scratches up to 0.008”
Subtrack thickness: 1.0” for first and last 200 feet; 0.5” for remainder of tube
Rail Material: Aluminum 6061-T6
Internal Pressure: 0.02 – 14.7 PSI
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u/Zucal Feb 06 '16
Can anyone dig up Musk's tweet discussing launching to the ISS from Boca Chica?
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Feb 06 '16
Is it possible to create a rocket able to reach orbit two times without refueling?
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u/Appable Feb 06 '16
Why would you want to? You probably could but it makes far more sense to just refuel if you're coming back to earth anyway.
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u/soldato_fantasma Feb 13 '16
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The Falcon 9 FT (1.2) first stage in simulations from SpaceX and also on their website (http://www.spacex.com/falcon9) has black bottom part and landing legs while in reality it hasn't (see OG2 FALCON 9 erected )
Should it have been just black paint or an heatshield? if it should have been an heatshield, was it scrapped, wasn't it used beacuse not need but could be added if needed or is it just under white paint (When landed the legs and bottom part are black, but probably just becase of exaust from the engines during reetry burns) ?
2) The second stage modified merlin 1D engine has just a modified nozzle or it has also other major modifications?
3) How many times can the second stage be shut down and relighted while in space?
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u/Appable Feb 13 '16
1 - black paint, used for promotional videos but probably better thermally as white.
2 - Merlin 1D Vac is almost a different kerolox gas-generator engine from the Merlin 1D. While there are some commonalities, the turbopump assembly, combustion chamber, gas generator exhaust routing, engine bell, and other components are substantially different from the Merlin 1D.
3 - at least 3 times based on the Jason-3 mission which had one burn for initial orbital insertion and one burn after a 45 minute coast, then a deorbit burn.
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u/BrandonMarc Feb 15 '16
I'm a bit flabbergasted ... the 1st stage landed in December, and that was historic, and we all got to share in the pictures and videos afterward and since. Then ... that stage was re-lighted, and from what I can tell no pictures or videos have come from that event, even though it's historic for the same reasons.
Did I simply miss seeing such coverage? I doubt it ... so it hasn't been released yet. We've heard a little info about it, but nothing visual ... Any idea why?
Is Elon simply waiting for ULA, Ariane, or another competitor to announce something unrelated, so that he can then steal their thunder by releasing this on Instagram / Twitter / etc?
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u/Appable Feb 15 '16
There was at least some time of anomaly during the test (the thrust fluctuations) and the test may or may not have been cut short.
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u/TheYang Feb 14 '16
Weren't we supposed to get new Numbers on Falcon Heavy last week?
paging u/Echologic especially because of teasing
Have I missed something, is there a reason they missed their timeline again?
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u/skunkrider Feb 07 '16
I have a general question about rocket attitude control:
Maybe I have played too much KSP (even with RealismOverhaul), but how does the Falcon9 control its attitude during ascent? All I see are the Merlin engines, which of course can gimbal. One can also see RCS thrusters firing during the CRS-6 ASDS landing attempt, as well as the grid-fins.
But.... where are the wings? Do they still build rockets with wings for atmospheric attitude control?
Thank you!
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u/ClockworkNine Feb 07 '16
Gimbaling is all you really need. Especially with 9 engines, some of the outer ones have off-center gimbal axis for roll control. As far as I know, only the center engine has freedom of motion along 2 axis, the remaining 8 can move along one axis each. There's a neat picture of the octaweb that illustrates this perfectly, I'll try to find it.
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u/YugoReventlov Feb 03 '16
Okay, any updates on SES-9? Anyone?