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

[refsmmat]

Jonathan is usually reliable. Maybe the Oberth Effect is Special K for some reason. ¯\_(ツ)_/¯ SpaceX probably has an operational reason for MVac burn at geosynchronous altitude if this is the case.

[Kabloona]

Jonathan is usually reliable. Maybe the Oberth Effect is Special K for some reason. ¯\_(ツ)_/¯ SpaceX probably has an operational reason for MVac burn at geosynchronous altitude if this is the case.

In the tweet must prior to the one I quoted, Jonathan said that the SpaceX info implied either (1) half of a 12 hr GTO orbit, or (2) a full 6 hr orbit of lower apogee. So clearly he doesn't have inside info that it would be option (1).

Then someone pointed out to Jonathan on Twitter that KSP shows escape burns at perigee are more efficient than at apogee, and Jonathan replied that, in effect, he didn't know offhand if you would gain anything by burning at perigee, but would have to run some calcs to check.

I know Jonathan is quite knowledgeable, moreso than I, but in this case yokem55 and Lou Scheffer are quite correct that a perigee burn does, in fact gain something.

So I persist in expecting Jonathan to follow up and realize that a perigee burn makes more sense.

[LouScheffer]

Jonathan is usually reliable.

Physics is even more reliable.   Plus the press kit quotes the GTO injection burn as 30 seconds.   That's not enough to reach GEO at apogee, which takes about a minute.

[the_other_Doug]

Didn't Musk state in his presser (or at east in one of Eric Berger's tweets) that they were doing this burn sequence to demonstrate direct injection to GSO?  You would do that by burning into orbit, then burning into GTO, then circularizing at apogee, right?

So, this would be a full simulation of that process, except, with such a light payload, they just keep firing until escape... and beyond...

[Kabloona]

Didn't Musk state in his presser (or at east in one of Eric Berger's tweets) that they were doing this burn sequence to demonstrate direct injection to GSO?  You would do that by burning into orbit, then burning into GTO, then circularizing at apogee, right?

So, this would be a full simulation of that process, except, with such a light payload, they just keep firing until escape... and beyond...

Berger did report that, but I think you may be taking his words too literally. Note that he said they were demonstrating a "burn sequence," not an actual GTO orbit.

All that really matters for direct injection to GSO is the demonstration of the 6-hr coast period. That's the crucial part of the "burn sequence." But for demonstration purposes, it doesn't really matter whether the 6 hr coast demo occurs in one entire sub-GTO orbit or half of a GTO orbit all the way up to apogee.

So as long as the engine restarts after the 6 hr coast, in whatever orbit, direct injection capability to GSO is, in effect, demonstrated.

Here's how Elon explained the 6 hr coast demo in the telecon. When he says "we do an initial burn to GTO," he means (I believe) in an Air Force direct GSO mission, not tomorrow's demo flight.

Elon Musk: Yeah, so the long coast is supposed to be designed to address the Air Force's need for a direct Geosynchronous Orbit insertion, meaning we do an initial burn to Geosynchronous Transfer Orbit, and then circularize at GEO, which is an approximately six hour coast. So that's the main reason for that long coast.

https://gist.github.com/theinternetftw/189852a3081eed7f695b80f374b8a727

(Thanks to theinternetftw for the transcription)

[henrylu]

Didn't Musk state in his presser (or at east in one of Eric Berger's tweets) that they were doing this burn sequence to demonstrate direct injection to GSO?  You would do that by burning into orbit, then burning into GTO, then circularizing at apogee, right?

So, this would be a full simulation of that process, except, with such a light payload, they just keep firing until escape... and beyond...

Nope, such burn profile certainly exceeds FH's capacity. The delta-v required for performing TMI from GTO apogee is enough to send the Roadster to Saturn directly form pregiee.

[Galactic Penguin SST]

Jonathan is usually reliable.

Physics is even more reliable.   Plus the press kit quotes the GTO injection burn as 30 seconds.   That's not enough to reach GEO at apogee, which takes about a minute.

He haven't seen the press kit yet at that time. Here is his updated analysis:

Took another look at trajectories given the press kit info. The 6 hour coast will demonstrate GEO insertion, but I do not believe the SECO-2 orbit will be geotransfer. (1/n)

If FH goes to a 200 x 35800 km x 24 deg GTO, it will be over the Indian Ocean at the time of the 3rd burn, at about 6h local time, pointing the wrong way. A burn then would send it to Venus, not Mars

Also, a burn from the apogee fo a GTO would be very inefficient compared to a burn at perigee

What makes more sense is a 6hr period orbit, with an apogee around 20000 km. That would allow a 3rd burn at perigee after 6 hr, and only 1.5 km/s required to get an aphelion near Mars. Still tweaking things to get the timings right.

[Kabloona]

Jonathan is usually reliable.

Physics is even more reliable.   Plus the press kit quotes the GTO injection burn as 30 seconds.   That's not enough to reach GEO at apogee, which takes about a minute.

He haven't seen the press kit yet at that time. Here is his updated analysis:

Took another look at trajectories given the press kit info. The 6 hour coast will demonstrate GEO insertion, but I do not believe the SECO-2 orbit will be geotransfer. (1/n)

If FH goes to a 200 x 35800 km x 24 deg GTO, it will be over the Indian Ocean at the time of the 3rd burn, at about 6h local time, pointing the wrong way. A burn then would send it to Venus, not Mars

Also, a burn from the apogee fo a GTO would be very inefficient compared to a burn at perigee

What makes more sense is a 6hr period orbit, with an apogee around 20000 km. That would allow a 3rd burn at perigee after 6 hr, and only 1.5 km/s required to get an aphelion near Mars. Still tweaking things to get the timings right.

Very good. So the consensus seems to be a 6 hr orbit with apogee around 20,000 km and 3rd burn at perigee.

[Galactic Penguin SST]

Jonathan is usually reliable.

Physics is even more reliable.   Plus the press kit quotes the GTO injection burn as 30 seconds.   That's not enough to reach GEO at apogee, which takes about a minute.

He haven't seen the press kit yet at that time. Here is his updated analysis:

Took another look at trajectories given the press kit info. The 6 hour coast will demonstrate GEO insertion, but I do not believe the SECO-2 orbit will be geotransfer. (1/n)

If FH goes to a 200 x 35800 km x 24 deg GTO, it will be over the Indian Ocean at the time of the 3rd burn, at about 6h local time, pointing the wrong way. A burn then would send it to Venus, not Mars

Also, a burn from the apogee fo a GTO would be very inefficient compared to a burn at perigee

What makes more sense is a 6hr period orbit, with an apogee around 20000 km. That would allow a 3rd burn at perigee after 6 hr, and only 1.5 km/s required to get an aphelion near Mars. Still tweaking things to get the timings right.

Very good. So the consensus seems to be a 6 hr orbit with apogee around 20,000 km and 3rd burn at perigee.

Also:

So my prediction is that the insertion burn will happen around 0050-0110 UTC Feb 7 about 300 km over Ecuador, sending the Tesla to an orbit with a=1.27, e=0.22, i=0.2, node 140, AOP 351. But these numbers are all probably plus or minus 50 percent

[Jamie T]

SpaceX CEO Elon Musk tells CNN Tech's Rachel Crane

[Ben the Space Brit]

Go Searcher is just now approaching Port Canaveral from the GovSat launch and presumably floating first stage recovery operations, so I assume that means it won't be on-site for any potential fairing recovery on the FH demo mission?

If they're doing fairing separation after the upper stage is in free flight, then the fairings will be coming down with much higher energy than on a Falcon-9 launch. It is possible that SpaceX's number crunchers have determined that them surviving re-entry and descent intact is low enough to make the effort of a search not cost-effective.

[Johnnyhinbos]

So - thoughts on who’s going to be MCing today’s webcast? Jim or one of the kids?

Also, given that this is ALL SpaceX (when was the last we saw that?) I’m sure they have some interesting camera remotes set up (I mean, beyond the obvious ones)

[tyrred]

It would be cool if all of the previous "hosts" each had a bit in this webcast.  Bonus points if Tim Urban, the Wait But Why guy, makes an appearance as well.

As a TMRO fan, I'm really anticipating the direction the whole production will take.  Bencredible, be with you.

[Ben the Space Brit]

My mother, whose normal response to spaceflight is "Yes, dear. Would you like a cup of tea?" is excited about today's flight too. She was amazed by previous footage of the booster landings and loved the ending tracking shot in the 'trailer' SpaceX published yesterday.

She says that Elon Musk is 'crazy' but she thinks it is the right kind.

[Johnnyhinbos]

So Tom Cross with Teslarati has put up some great closeups of the FH, including one of one of the nosecones and longeron. Some great details there, like I didn’t think about how the nosecone has its own umbilical but of course makes perfect sense. The strut connection to the side booster - it looks so, permanent. Like it’s not meant to detach. Looking forward to seeing closeups of that area post landing (for many reasons). 

It’ll also be cool to see a landed stage with a top - it’ll look more complete...

https://twitter.com/_tomcross_/status/960661318649962496

[Satori]

On the press-kit there is a reference to a third stage. Is this an error? They are talking about a third burn of the second stage? Or ir there really a small third (kick) stage?

[kevinof]

My understanding is that it's not a 3rd stage - just a 3rd burn after a long 6 hour coast.

On the press-kit there is a reference to a third stage. Is this an error? They are talking about a third burn of the second stage? Or ir there really a small third (kick) stage?

[Ben the Space Brit]

On the press-kit there is a reference to a third stage. Is this an error? They are talking about a third burn of the second stage? Or ir there really a small third (kick) stage?

Outboard boosters + core = stage 1
Core only = stage 2
Upper stage = stage 3

I believe that D-IVH uses similar terminology.

[Satori]

On the press-kit there is a reference to a third stage. Is this an error? They are talking about a third burn of the second stage? Or ir there really a small third (kick) stage?

Outboard boosters + core = stage 1
Core only = stage 2
Upper stage = stage 3

I believe that D-IVH uses similar terminology.

Ah! Makes sense! Thanks!

[hopalong]

On the press-kit there is a reference to a third stage. Is this an error? They are talking about a third burn of the second stage? Or ir there really a small third (kick) stage?

Outboard boosters + core = stage 1
Core only = stage 2
Upper stage = stage 3

I believe that D-IVH uses similar terminology.

I read it as the third burn of the second stage, which is in line with the 2nd stage burns at 03:15 and 28:22.
Not well worded.