SpaceX Falcon 9 FT launch - EchoStar 23 - LC-39A

[dhanson865]

Can someone please explain what 'hot landing' means?

It takes less fuel to brake at the last possible instant before landing (the term involved in that math is "gravity losses"). Because of this the faster the booster is traveling at altitude the faster it'll be 1 second before landing and or the less fuel they have left the faster it'll come in for landing. They'll burn as hard as necessary the last possible moment to conserve fuel.

Softer landings have lots a fuel leftover from the lighter payload for that mission and use one engine for a longer burn and come in slower. Less risk, less stress, more likely to be able to reuse that first stage.

Harder landings have less fuel leftover from a heavier payload to orbit (or a payload to a higher orbit) and use 3 engines to burn less time but put out more thrust (3 times the engines at more than minimal thrust means more than 3 times the heat). The engines can be run at a wide throttle range so there is a big difference in exhaust flames/temperature of the engine bell depending on throttle amount and length of the burn in time.

It's not just an expression there literally is more stuff burning / more flames at the last second if the booster is "coming in hot". It also puts more stress on the rocket in terms of heat, vibration, G force during burn, and possibly at time of impact (when it actually touches down).

 

[ecarfan]

Can someone please explain what 'hot landing' means?

In this case it means that if SpaceX attempted to land the first stage for this particular launch the stage would undergo a RUD* upon touchdown.

*Rapid Unscheduled Disassembly

 

[Electroman]

#21dhanson865 - Thanks for the explanation. Appreciated.

 

[Grendal]

There have been two "hot landed" boosters: JCSAT 14 and Thaicom 8. The 3rd and 4th recovered boosters. Thaicom 8 was the booster that landed hard enough to crush the landing leg core and it came back with the pronounced tilt.

JCSAT 14 is permanently at McGregor for stress testing and further abuse under the premise that if the most abused booster can take it then less abused ones should do even better. It has been fired more than any other booster. It has had at least 12 full launch length burns.

Thaicom 8 will be reused, maybe, as one of the Falcon Heavy side boosters for the test launch sometime this year.

 

[ggr]

Can someone please explain what 'hot landing' means?

A bit more detail: If they can, based on the payload and orbital destination, they have enough fuel left in the first stage to actually reverse its direction, re-enter the atmosphere "slowly" (couple thousand km/h) and Return to Launch Site (RTLS). For a lot of Geosynchronous (Clarke) orbit launches, they don't have enough fuel left to do that, so they don't try to turn it around, they just slow it down some, and land on one of the barges. But for the heaviest of payloads to Geo orbit, they don't have quite enough fuel even for that. So, a "hot landing": they do a burn to bring it back down, but don't slow the re-entry very much, and then at the very last seconds, re-light 3 engines (normally just one) to slow it down really quickly for the barge landing. This saves a bit of fuel. They didn't expect the booster to survive re-entry the first time they tried this, but it did, and it is now the subject of very extensive testing. The fourth alternative is what's happening this time; not even trying due to insufficient remaining fuel.

(snarky comment: watch the media label this as a "failed landing"!)

 

[Electroman]

It will be nice to plot a speed vs altitude graph for hot and normal landing.

 

[dhanson865]

It will be nice to plot a speed vs altitude graph for hot and normal landing.

If you go back to youtube and watch the technical or hosted broadcasts you can get altitude and speed data to graph yourself if you like. If not you could probably post in r/spacex and someone would do it for you or point you to preexisting graphs.

Every landing has been televised/recorded in some way so there is plenty of publicly available data.

 

[Electroman]

If you go back to youtube and watch the technical or hosted broadcasts you can get altitude and speed data to graph yourself if you like. If not you could probably post in r/spacex and someone would do it for you or point you to preexisting graphs.

Every landing has been televised/recorded in some way so there is plenty of publicly available data.

The data that get displayed on our screens is the telemetry data of the ascending first stage followed by 2nd stage. No telemetry data is shown to the public for the first stage after the separation of 2nd stage.

 

[dhanson865]

The data that get displayed on our screens is the telemetry data of the ascending first stage followed by 2nd stage. No telemetry data is shown to the public for the first stage after the separation of 2nd stage.

I thought I saw a second set of telemetry on some views but it's a lot a video to review to find it.

It may be that you can't get that information for the return to landing site or drone ship.

I've seen similar math done for spacex before like Orbcomm2LaunchData which has the data from the Orbcomm2 webcast graphed.

http://i.imgur.com/sM5rd93.png and http://i.imgur.com/6gAaya0.png will give you some insight on to how hard it is to do a hot landing vs soft as it compares speed and acceleration for a few different launch profiles to MECO (separation speed should be very close to that).

 

[Grendal]

Aargh, pushed back again. Still having delays on finishing LC-39A.

Chris B - NSF on Twitter

"NET February 3 (Window opens 00:07). Emphasis on the NET."

So Friday, February 3rd at 12:07 AM (9:07 PM PST) with the same two and half hour launch window.

 

[Electroman]

I thought I saw a second set of telemetry on some views but it's a lot a video to review to find it.

It may be that you can't get that information for the return to landing site or drone ship.

I've seen similar math done for spacex before like Orbcomm2LaunchData which has the data from the Orbcomm2 webcast graphed.

http://i.imgur.com/sM5rd93.png and http://i.imgur.com/6gAaya0.png will give you some insight on to how hard it is to do a hot landing vs soft as it compares speed and acceleration for a few different launch profiles to MECO (separation speed should be very close to that).

Thanks for those links. Interesting, but I guess I am having trouble reading it. Specifically i am looking at the Speed vs. Time graph to see how the deceleration happens. Here is that graph below :

- In this graph where does MECO happen?

- Is it fair to assume that positive speed is ascending and negative speed is descending? If so graphs get even more confusing. Orbcomm2 (red line) does not even have negative speed, whereas the others have some, but again it doesn't add up.

Some critical information is missing and not marked?

 

[Grendal]

Thanks for those links. Interesting, but I guess I am having trouble reading it. Specifically i am looking at the Speed vs. Time graph to see how the deceleration happens. Here is that graph below :

View attachment 211842

- In this graph where does MECO happen?

- Is it fair to assume that positive speed is ascending and negative speed is descending? If so graphs get even more confusing. Orbcomm2 (red line) does not even have negative speed, whereas the others have some, but again it doesn't add up.

Some critical information is missing and not marked?

I believe that MECO happens at the first peak. The major difference and why Orbcomm 2 is so different is that it was a RTLS. So it turned around and boosted back to the landing site at altitude maintaining speed. For an ASDS landing the booster immediately drops into the atmosphere and loses speed. I am confused at the negative speed under my reasoning though.

 

[dhanson865]

I believe that MECO happens at the first peak. The major difference and why Orbcomm 2 is so different is that it was a RTLS. So it turned around and boosted back to the landing site at altitude maintaining speed. For an ASDS landing the booster immediately drops into the atmosphere and loses speed. I am confused at the negative speed under my reasoning though.

I think all the speeds are for the complete rocket or stage 2 plus payload. Thus there wouldn't be any burnback in those graphs.

Orbcomm2 is so different because it was a geostationary final destination near the max payload that Falcon9 could get to that high an orbit.

The higher orbit SpaceX could give means less time to get the satellite to it's final orbit and the less fuel the satellite has to spend to get there (leaving more fuel for station keeping) thus extending the operating life of the satellite.

Essentially that mission had a higher altitude target so they burned harder/longer/different pitch anything they had to, to get the rocket up there.

SpaceX over delivered on altitude as a way to make up for the fact that the launch schedule had been delayed previously. I'm sure they got a few brownie points back that they had lost previously for doing so.

 

[dhanson865]

Thanks for those links. Interesting, but I guess I am having trouble reading it. Specifically i am looking at the Speed vs. Time graph to see how the deceleration happens. Here is that graph below :

View attachment 211842

- In this graph where does MECO happen?

- Is it fair to assume that positive speed is ascending and negative speed is descending? If so graphs get even more confusing. Orbcomm2 (red line) does not even have negative speed, whereas the others have some, but again it doesn't add up.

Some critical information is missing and not marked?

You can use http://i.imgur.com/6gAaya0.png and the other pictures as the key for when the MECO/stage separation happens around 140 seconds in.

All of the data is ascending as this doesn't have data for the return of the first stage.

The "deceleration" is atmospheric and is practically speaking a lack of acceleration while the first stage is off and the second stage hasn't fired yet. Or at the end of the graph it's absolutely lack of acceleration when the rocket is in the parking orbit.

Also the object of putting something into orbit is to get it traveling horizontally really really fast. Once you are high enough you can be increasing speed and decreasing altitude but still working on getting into the desired orbit. Essentially all the lines zero out at the right of that graph when the exact orbit is reached.

I only mentioned it as the ground speed, distance, altitude all give you clues as to how severe the landing burn will have to be. Not a 1:1 correlation but still clues.


For a full explanation of the graphs you might want to ask u/only_to_downvote who posted those see

Webcast telemetry data from the recent Orbcomm2 launch • /r/spacex and
Transcribed Webcast Launch Data • /r/spacex

 

[Electroman]

Thank you. So this means none of these graphs provide any telemetry data for stage 1 after MECO.

Perhaps SpaceX never released that data, so all we can do is make some guesswork based on the lateral speed, altitude and distance during separation. That would be an interesting exercise, but not that useful like actually seeing the real data.

 

[Grendal]

I think all the speeds are for the complete rocket or stage 2 plus payload. Thus there wouldn't be any burnback in those graphs.

Orbcomm2 is so different because it was a geostationary final destination near the max payload that Falcon9 could get to that high an orbit.

The higher orbit SpaceX could give means less time to get the satellite to it's final orbit and the less fuel the satellite has to spend to get there (leaving more fuel for station keeping) thus extending the operating life of the satellite.

Essentially that mission had a higher altitude target so they burned harder/longer/different pitch anything they had to, to get the rocket up there.

SpaceX over delivered on altitude as a way to make up for the fact that the launch schedule had been delayed previously. I'm sure they got a few brownie points back that they had lost previously for doing so.

I think you're mixing up Orbcomm 2 with SES-9.

Orbcomm 2 was a very light LEO satellite. That is why it could do a successful RTLS.

SES-9 was the delayed GTO satellite that SpaceX did the extra long burn for and ultimately lost the booster on a failed ASDS attempt. They definitely got the brownie points and SES is willing to be the first to use a used booster.

JCSAT14 was a GTO satellite of similar weight to the SES-9 but was successfully recovered.

List of Falcon 9 and Falcon Heavy launches - Wikipedia

I just noticed on the list that the Iridium payload was incredibly heavy but is just to LEO which allowed for the successful ASDS landing in spite of the significantly heavier payload.

Back to EchoStar. It weighs in at over 12,000 lbs which would make it the heaviest GTO launch to date. The new loading procedures cause a small loss in fuel which is what puts this satellite just over the top. Also SpaceX might be giving it a similar extra boost like it did for SES-9 because of the delay from the anomaly.

 

[Blip]

Sorry to off-topic, but this was funny: xkcd: Barge

 

[dhanson865]

I think you're mixing up Orbcomm 2 with SES-9.

Orbcomm 2 was a very light LEO satellite. That is why it could do a successful RTLS.

I was mixing up the flavor text, but maybe not as much as you think.

Orbcomm2 mission is otherwise known as Falcon 9 Flight 20 - Wikipedia and the reason it burned so high was for geosynchronous orbit but it was after deploying the payload as a test/demonstration only.

Second stage re-ignition
Following successful launch and deployment of the OG2 satellites, the Merlin Vacuum (1D) second-stage engine successfully re-ignited, demonstrating its capability to launch SES-9 into geostationary transfer orbit.

So it was related to SES9 and the brownie points (and why it stuck in my head) but it wasn't the actual SES9 delivery mission.

Also Orbcomm2 on flight 20 was 11 satellites, each one was very light but on a whole was a heavy load, not max but well above average.

 

[macpacheco]

SpaceX is still working on the pad. Delayed to early February. Only when the static fire happens, we can have confidence in launch dates given.

 

[macpacheco]

TEL (Transport Erector Launcher) seen upright at LC39A. SpaceX seems to be making good progress. I *think* launch sometime next week now likely.