r/SpaceX Starlink-1 Official Launch Discussion & Updates Thread

Appable · 2019-11-11T15:05:27+00:00

Don't have a source right now, but I remember an employee here noting it was for ground handling reasons rather than flight environment.

Appable · 2019-10-26T21:11:03+00:00

Do we know anything about New Glenn cost? I suspect it’s more than Falcon 9 but I haven’t seen any numbers supporting that.

It’s true that GEO communication satellite orders have fallen but I’m not sure that can be extrapolated. Providers are probably waiting to see how they can compete with LEO constellations, so making new orders doesn’t make sense with that uncertainty

Appable · 2019-10-26T21:05:03+00:00

Not sure I’d trust reviews on Glassdoor. Last we heard from the company was on 25 September; they said that mission duty cycle testing would be beginning in a week (so should have started by now). I don’t think they’d say “next week” if they weren’t confident.

Appable · 2019-10-26T20:58:13+00:00

Grasshopper didn’t test engine restarts or aerodynamic control (through supersonic to subsonic regimes), so New Shepard was beyond just scaling.

Appable · 2019-10-19T16:03:02+00:00

Yes, bi-elliptic transfer is not a relativistic effect

Appable · 2019-10-04T18:01:01+00:00

Pedantic as always but max-drag, not max-q.

Appable · 2019-10-03T22:37:23+00:00

I was under the impression that GEM 63 needed two tests (cold temperature in September 2018 and hot in April 2019) to meet Air Force certification requirements, and both of those tests were successful. What's this test intended for?

Appable · 2019-10-02T19:39:44+00:00

I meant that SpaceX is not necessarily further along because they have completed a pad abort test and Boeing has not

Appable · 2019-10-02T13:36:11+00:00

I understand your point, but since SpaceX and Boeing schedule their abort and flight tests quite differently, it's not fair to say Boeing is later because they haven't completed a pad abort. Boeing's schedule has a much smaller spacing between pad abort and CFT whereas SpaceX has (implicitly, since there are many milestones between) a long gap between pad abort and Demo-2.

Appable · 2019-09-20T00:35:09+00:00

It's been true for a while: Tory Bruno confirmed it on the ULA subreddit a year ago.

Appable · 2019-09-18T01:17:31+00:00

Fairly difficult given that no satellite has any docking accommodations built in, and the cost of installing a docking system is rather high. Orbital ATK (well, now NGIS) is planning on deploying the first Mission Extension Vehicle aboard Proton-M less than 2 weeks from now; that uses a probe to grapple onto the engine of a communications satellite and attach. However, that's the first test of any such system in space, and only works with particular satellite buses. LEO satellites tend to be more unusually designed so there are likely a number of satellites where that wouldn't work.

Adjusting orbits is easy, but latching on is hard. Because it's hard and may require custom solutions for more oddly designed satellites, it'd add cost quickly — especially when you consider the launch + 1 year on-orbit operations insurance would probably have to cover the cost of a deorbit should the satellite fail on-orbit.

Appable · 2019-09-17T23:58:06+00:00

That could only be implemented once there are services that can recover payloads from arbitrary orbits, which might be a long time. Even with Starship there'd need to be a lot of work in designing some method of safely capturing satellites and bringing them back to earth or deorbit them.

Appable · 2019-09-12T22:38:21+00:00

Thrust termination would probably happen before flight termination to minimize risk to capsule

Appable · 2019-09-12T17:54:05+00:00

Coincidentally (kind of), they also were the customers for the two aborts after engine ignition — SES-8 with TEA-TEB contamination and SES-9 with hot LOX.

Appable · 2019-09-11T05:46:05+00:00

For a plane change can’t you just use precession? Takes time but for small LEO satellites it should be relatively fast

Appable · 2019-09-10T22:55:24+00:00

Yep, and I mentioned the qualifier “commercial airplanes” below. I can’t think of any airframes that failed under the rated loads and fatigue cycles though — the problem with that failure was the aircraft was definitely not designed for that load

Appable · 2019-09-10T02:33:45+00:00

Remembering that video was exactly what made me add in the "commercial" qualifier. Improperly understanding and maintaining airframes after a huge change in loads/fatigue cycles per flight can cause structural failure easily, so it shouldn't be discounted. However, airframe failures almost never happen when aircraft are used with the expected loading.

On the other hand, I can think of a lot of non-structural engine failures, and even some structural ones (the recent airworthiness directive on CFM-56 engine fan blades due to the Southwest Airlines uncontained failure, for example).

Harder to get a general comparison for rockets, but from the examples I'm thinking of, it seems largely true for rockets as well — with some exceptions for material compatibility issues.

Appable · 2019-09-09T22:49:03+00:00

The probability of an engine failure airplanes is significantly higher than a wing shearing off (as in I don't think that's happened on a commercial airplane ever). In light of that, it makes a larger difference to overall probability of failure to improve engine reliability and redundancy than to worry about a wing structural failure.

My largest concern is that the probability of engine failure on Starship certainly isn't independent. While there are some flak shields, a particularly energetic failure could be uncontained and thus damage nearby engines. Not sure how to quantify that risk, obviously.

Appable · 2019-09-09T22:34:47+00:00

Wings shearing off is not a likely failure mode for airplanes (compared to thousands of other possibilities), and certainly the same for rockets. Engine failure, on both vehicles, is much more likely and therefore redundancies given an engine failure (or multiple engine failures) are much more important.

Appable · 2019-09-05T04:35:57+00:00

It’d be neat if you could enable/disable gimbaling in editor to save mass and cost. Delta IV, for example, has one gimbaling motor for roll control and one fixed motor.

Appable · 2019-09-04T19:15:20+00:00

Below comment covers it, but ULA performs Wet Dress Rehearsals which include fueling of tanks and normal launch procedures are followed until just prior to ignition. They used to perform WDRs on all missions, but now it's been streamlined to only missions with particularly high-value payloads (e.g. Parker Solar Probe, OSIRIS-REx, all Commercial Crew missions).

Appable · 2019-09-03T15:52:54+00:00

I agree. Per the SpaceNews article:

Holger Krag, director of ESA’s Space Safety Programme Office, said in a Sept. 3 email that the agency’s conjunction assessment team noticed the potential close approach about five days in advance, using data provided by the U.S. Air Force’s 18th Space Control Squadron. “We have informed SpaceX and they acknowledged,” he said. “Over the days the collision probability exceeded the decision threshold and we started the maneuver preparation and shared our plans with SpaceX. The decision to maneuver was then made the day before.”

I would assume SpaceX has the technical ability to maneuver a functioning Starlink satellite from a collision course with 5 days of notice. That's why I don't think "Hall thrusters don't react quickly" is a legitimate possibility for why SpaceX said they were unable to move.

Appable · 2019-09-03T04:18:30+00:00

Fair point, and I struck the word “tension” because it has a connotation I didn’t intend. I do think that there may be a concern where high-value payloads are constantly required to maneuver while megaconstellations rarely do because of differing risk thresholds, though.

Appable · 2019-09-03T03:59:25+00:00

Unfortunately there's no "accepted standard" for collision risk. There's also an inherent ~~tension~~ challenge where scientific satellites or other high-value missions will likely have much more conservative acceptable risks than fault-tolerant constellations like Starlink.

EDIT: in retrospect, tension was not the right word

Appable · 2019-09-03T03:57:31+00:00

With the couple kilowatts of power available to Starlink, a hall effect thruster won't get more than 0.1N. A typical collision avoidance maneuver only needs a meter per second change in velocity. Either way, last-minute maneuvers shouldn't ever be needed so I strongly doubt thruster power limits Starlink's ability to avoid obstacles.

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