SpaceX FH : Falcon Heavy Demo : Feb 6, 2018 : Discussion Thread 2

[tvg98]

I just noticed that the live stream of Starman is still going. Is it live or recorded? I thought the batteries would have died by now...

What you're seeing is a replay of the stream.

[Jimmy_C]

That's a really cool shirt! I wish there was a way to get one.

[alang]

I didn't find this information anywhere: Did the roadster separate from the second stage or is it still attached?

AFAIK, I'm not sure there is definitive information but consensus is almost certainly they remain attached.  No reason to separate.

Confirmation (or as close as I've seen so far) that the 2nd stage remains attached:

https://twitter.com/planet4589/status/961709147229229059

The source who told me this is a senior SpaceX person who would know. There was no separation from stage 2.

Thanks for the clarification. Should this information go to the update thread?

It isn't  an update.  It's been known for awhile.  Plus it makes no sense to separate.

Probably no good reason to add the complexity of a payload adapter that could separate it properly
 I don't know but I suspect that avoiding imparting spin on a payload during separation is not that trivial.
For a payload where you want to take images of the earth in the background as in this case then having it part of a stage that is under control was probably an important consideration.

[nicp]

Forgive me if this has been discussed elsewhere, long day and my brief search turned up nothing.
Does anyone have a clue why the FH Center didn't make it? I've read and heard various theories, lack of TEA/TEB to me does not add up - I see no reason why the center core would need more of that than for any F9.

Lack of propellant - more plausible, but seems pretty easy to model. SpaceX can do arithmetic. Well ok, the blooper reel has one that runs out _right_ above the ASDS..

Somewhere - and I can't find it now - there was a comment re the grid fins - perhaps they fried. Aluminium grid fins... But again, SpaceX know the limits of the vehicle, a longer entry burn should sort that out, slow things sufficiently for the fins and the stage to handle it. But then maybe that could couple into a lack of fuel... No. Too easy to calculate.

I don't get it. The factors that are 'out of the ordinary' for an F9 seem so easy to model I can't see SpaceX screwing them up.

[Robotbeat]

Who knows. Could be just random that it used more TEA/TEB, like a stuck valve or something.

[zeke01]

Did GOES-16 spot the launch? The time certainly matches.

http://col.st/l6XAy


Edit: Ugh, forgot to mention to press the spacebar to play the short movie

Yes. http://cimss.ssec.wisc.edu/goes/blog/archives/26936

[OxCartMark]

Request to the video creating people out there:

The launch was so utterly identical to the animation we've had for the last few years that I think it would be awesome if someone edits together a split screen of actual vs. prediction for the parts that have video for both.  That would make for a shorter video that you could show someone less interested to give them an idea of what just happened and it would show how with solid engineering work really far out dreams can come true.

[Robotbeat]

BFS uses a completely different ignition technology. And has a lot more redundancy on landing.

[Barrie]

Does TEA/TEB work by administering a fixed dose which is presumed to work, or is there a continuous feed until ignition is detected?

[intrepidpursuit]

FH center core is a new vehicle. Landings haven't always worked on the first try and obviously something was different here and the model didn't match the test. They've never had the same failure twice and they won't start now. BFR is even more different and probably won't work flawlessly on its first test. Comparing FH center core relighting its merlins to Crew Dragon is just nonsense.

[rickl]

One thing I haven't seen discussed:  Is there any other example of a rocket putting a payload into solar orbit on its first flight?  How about lunar orbit or hitting the moon?

[FinalFrontier]

Curious question. Would be interested to know if any estimates of maximum velocity achieved currently exist. Would be cool to see exactly what the top speed of the world's fastest car was and also, if there are any current velocity estimates.

[hybridsix]

Hey everyone... new to the forums as a contributor.

I took some photos of the launch from the Turn Basin viewing site, I was fortunate enough to have a good friend of mine who works for NASA get me in on her car pass for the launch.

Hope you enjoy!

Flickr Album: https://flic.kr/s/aHsmcvWyVv

[LouScheffer]

Looking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core.

They only ran the center core 30 more seconds (side cores 2:34, counting early ignition, center core 3:04) so the average throttle down during 3 core operation was 80% (assuming 100% for 30 seconds after separation, they took 2:00 fuel while to side cores took 2:30).   They appear to have done this right from the beginning, as the center core plume is about 80% as long right from the start.

So it seems they could run a much better (though more complicated) profile.  Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more.  A back of the envelope calculation indicates this would help a lot.  The thrust during the first period would be reduced by about 2.6/2.8 (counting a core as 1.0.  The center would give 1.0 for 1/5 of the time, 0.5 for 4/5 of the time, for a total of 2.6, as opposed to the apparent 80% used on this flight).  Since staging velocity was about 2634 m/s, this would be reduced by about 200 m/s.  This is approximate since there might be additional gravity losses (but that's why I suggested full thrust for the first 0:30) but on the other hand the side boosters have an easier boostback.

But judging by Intelsat 35, the last minute of the core stage gives about 700 m/s more than the last 30 seconds alone, for a net gain of 500 m/s at core staging.  They would need to reserve some of this for additional core re-entry slowing, but the gain is still significant.

This translates into a big gain in payload.  If the second stage needs to provide less delta-V, it can loft a heavier satellite.  For example, changing the payload from 8 tonnes to 10 tonnes costs about 450 m/s, using the usual assumptions (isp = 348, empty mass 4.5t, fuel = 111.5t).   So SpaceX could get about a 20% increase in payload just by changing the throttle profile.

[catdlr]

Curious question. Would be interested to know if any estimates of maximum velocity achieved currently exist. Would be cool to see exactly what the top speed of the world's fastest car was and also, if there are any current velocity estimates.

After a five-year jaunt through space, NASA's robotic Juno spacecraft arrived at Jupiter on July 4, 2016, and the gas giant's impressive gravity accelerated the probe to approximately 165,000 mph (265,000 km/h) relative to Earth. This made Juno the fastest-moving human-made object in history.

In terms of pure heliocentric velocity, NASA's Helios I and Helios II probes previously held the record at 157,000 mph (253,000 km/h) as they passed by the sun. These probes were launched in 1974 and 1976, to study solar processes.

The record for fastest launch velocity belongs to the New Horizons probe, which lifted off in 2006 on a mission to Pluto and the Kuiper Belt. This 1,054-lb. (478 kilograms), piano-size spacecraft sped away from the Earth at a blistering pace of 36,000 mph (almost 58,000 km/h).

New Horizons' escape speed from Earth beat the previous record of 32,400 mph (about 52,000 km/h), set when Pioneer 10 set out for Jupiter, in 1972.

And though Juno is currently the fastest human-made object, it remains to be seen how long the space probe can hold onto the impressive title. Solar Probe Plus, a NASA mission scheduled to launch in 2018, is designed to fly into the sun's atmosphere, making it the first probe to do so. Due to the enormity of Earth's nearest star, the probe is expected to reach orbital velocities as high as 450,000 mph (724,000 km/h). For perspective, at this speed, you could travel from the Earth to the moon in about 30 minutes.

For spacecraft that have re-entered Earth's atmosphere, the highest speed was set by the comet-catching Stardust spacecraft, which plunged back toward Earth at a speed of 29,000 mph (more than 46,600 km/h).

source: https://www.livescience.com/32655-whats-the-fastest-spacecraft-ever.html

[Steven Pietrobon]

Enhanced images of the higher res pics posted by SpaceX. Spot the photoshop!

[Lars-J]

What an outrage!

[JAFO]

Forgive me if this has been discussed elsewhere, long day and my brief search turned up nothing.
Does anyone have a clue why the FH Center didn't make it?

I remember reading that the returning boosters were targeted slightly away from the LZ, that way in case the engines didn't relight the booster would not impact the barge/LZ, and if they did relight the booster would make a quick course correction for the center of the LZ/barge.

When I saw the big cloud obscuring the barge and the video cutout my immediate reaction was "Missed it by THAT much!" Can't wait to see the video.

[deruch]

Looking at the launch pictures and timeline, it looks like SpaceX used an extremely conservative throttle profile on the middle core.

They only ran the center core 30 more seconds (side cores 2:34, counting early ignition, center core 3:04) so the average throttle down during 3 core operation was 80% (assuming 100% for 30 seconds after separation, they took 2:00 fuel while to side cores took 2:30).   They appear to have done this right from the beginning, as the center core plume is about 80% as long right from the start.

So it seems they could run a much better (though more complicated) profile.  Perhaps full power for 30 sec, then half power for 2 minutes, separate, then full power for a full minute more.  A back of the envelope calculation indicates this would help a lot.  The thrust during the first period would be reduced by about 2.6/2.8 (counting a core as 1.0.  The center would give 1.0 for 1/5 of the time, 0.5 for 4/5 of the time, for a total of 2.6, as opposed to the apparent 80% used on this flight).  Since staging velocity was about 2634 m/s, this would be reduced by about 200 m/s.  This is approximate since there might be additional gravity losses (but that's why I suggested full thrust for the first 0:30) but on the other hand the side boosters have an easier boostback.

But judging by Intelsat 35, the last minute of the core stage gives about 700 m/s more than the last 30 seconds alone, for a net gain of 500 m/s at core staging.  They would need to reserve some of this for additional core re-entry slowing, but the gain is still significant.

This translates into a big gain in payload.  If the second stage needs to provide less delta-V, it can loft a heavier satellite.  For example, changing the payload from 8 tonnes to 10 tonnes costs about 450 m/s, using the usual assumptions (isp = 348, empty mass 4.5t, fuel = 111.5t).   So SpaceX could get about a 20% increase in payload just by changing the throttle profile.

Is this likely to have much effect on the timing/magnitude of Max-Q?

[Kaputnik]

Forgive me if this has been discussed elsewhere, long day and my brief search turned up nothing.
Does anyone have a clue why the FH Center didn't make it?

I remember reading that the returning boosters were targeted slightly away from the LZ, that way in case the engines didn't relight the booster would not impact the barge/LZ, and if they did relight the booster would make a quick course correction for the center of the LZ/barge.

When I saw the big cloud obscuring the barge and the video cutout my immediate reaction was "Missed it by THAT much!" Can't wait to see the video.

It's not really a question of targeting to miss, simply that the incoming booster cannot be in a ballistic trajectory that hits the ASDS/LZ. It's coming in from the side, so a successful burn will drop it onto the ASDS/LZ by default