OHM TESS

[OrbitHangar]

Author: brianj

The Transiting Exoplanet Survey Satellite (TESS) spacecraft and launch scenario for 18 April 2018 (1st stage flyback to ASDS).

Installation and operation notes in /Doc/TESS

 

REQUIRED ADD-ON

"Falcon9 for Orbiter2016"
https://www.orbithangar.com/searchid.php?ID=7091



DOWNLOAD

 

[Kyle]

Thank you, Brian!

 

[IronRain]

Thanks Brian!

 

[BrianJ]

My pleasure, hope it's useful

 

[BrianJ]

SpaceX TESS launch press kit is online:
http://www.spacex.com/sites/spacex/files/tesspresskit.pdf

No mention of any 1st stage "boostback" burn - so Entry and Descent burns only?

If that is the case, I guess the parking orbit will be more like 200km x 600km (if they really are targeting a 600km PeA at final orbit insertion).

Fairing(s) will have parafoil but no attempt to actually catch them this time, apparently.

Good luck TESS and SpaceX teams :thumbup:

 

[Marijn]

The current location of the drone ship would tell whether they are planning doing a boostback or not? Perhaps some maritime warning site will disclose that info.

Check Musk's Twitter. It looks like they will try something new. Recovering the upper stage with a giant party balloon? Sounds like fun.

 

[BrianJ]

The current location of the drone ship would tell whether they are planning doing a boostback or not? Perhaps some maritime warning site will disclose that info.

From Reddit, ASDS location West 77.506 North 28.874, final orbit insertion 200km x 275,000km.

That would suggest parking orbit of 200km x 200km at 29.5deg inc.
The ASDS seems a bit close for an EDL-Only burn profile, but who knows. Will find out soon, hopefully

The Falcon9 add-on needs a fuel-reserve of ~70000kg to put the 1st stage near the ASDS, but then it's way too heavy on the way down.
Maybe it'll work better if I offload some fuel first. Or change 1st stage ApA.

Check Musk's Twitter. It looks like they will try something new. Recovering the upper stage with a giant party balloon? Sounds like fun.

Not sure what he's on about there. Inflatable heatshield for 2nd stage? Haven't heard anything about it with regard to this launch, certainly.

Cheers,
BrianJ

 

[Marijn]

Not sure what he's on about there.

'And then land on a bouncy house'. Something very interesting is coming up it seems. Something somehow was not picked up by any media. I really enjoy how details gradually become available. It must be hard to keep up with this as an add-on developer

 

[boogabooga]

Gonna have to update the launch date...

Also, has anyone pulled-off TESS's super-interesting trajectory?

 

[Marijn]

Aww. I was just ready for it. What's the problem? Weather?

 

[Urwumpe]

Aww. I was just ready for it. What's the problem? Weather?

Nothing known. Last tweet by SpaceX was:

Standing down today to conduct additional GNC analysis, and teams are now working towards a targeted launch of @NASA_TESS on Wednesday, April 18.

 

[BrianJ]

Gonna have to update the launch date...

v.180417 updated on OH with new launch scenario.
Now uses reported ASDS position, 200km parking orbit, 29.5deg.inc., 1st stage Flyback-EDL to ASDS.

The ASDS is less than 1/2 the usual distance from LC-40, for 1st stage EDL-Only burn profile. Can't see how they can do it unless they offload >50mt propellant. I'm betting there is a Boostback burn.

Also, has anyone pulled-off TESS's super-interesting trajectory?

Yep, targeted a 40deg.inc.(ecliptic) Earth orbit at 17 x 59 earth-radii, thats ~ 108000km x 375000km
That didn't look too stable on a 1yr plot(LagrangeMFD) so I pushed the ApA back out to 440000km and it looks pretty solid.
Orbit period/lunar resonance is the important thing, I think.
I must have hit the Moon a bit fast, needed to do a hefty retrograde burn at 1st Perigee after flyby to pull the ApA down. Still had >240m/s dV remaining.

It must be hard to keep up with this as an add-on developer

SpaceX trying out every idea they can come up with, simply for the fun of it I think. We await the "party balloon and bouncy castle" trick.

 

[Marijn]

v.180417 updated on OH with new launch scenario.
Now uses reported ASDS position, 200km parking orbit, 29.5deg.inc., 1st stage Flyback-EDL to ASDS.

Thanks again for the quick updates. I am having lots of fun with it. All systems and weather are go at the moment, so hopefully we'll see in a few hours how they do it and what surprises are in store. My guess is that they will test some kind of ballute to slow the upper stage down.

Wy did you choose 29.5 deg inc.? Because of the reported ASDS position? Otherwise I would expect 28.6 degrees inc. like the base latitude to be optimal.

And do you know what inc. the final orbit has after the lunar gravity assist? I think I read 37 degrees somewhere, but I am unsure if that's correct and what reference plane is used. Since TESS remains a satellite of earth, it makes sense to me that the equatorial plane is ment.

---------- Post added at 08:31 PM ---------- Previous post was at 08:17 PM ----------

We await the "party balloon and bouncy castle" trick.

I am trying to make some sense of what Musk said on Twitter. My thoughts at the moment: It's gonna be a big ballute, some sort of an inflatable cone which extends from the back which will create drag and slow it down. When it has slowed down, a parachute will deploy from the other side. It will splashdown with the ballute on the bottom side. That's the bouncing castle. And the upper-stage falls into the ballute to keep it dry.

 

[BrianJ]

@Marijn
Hi,
yep, hope all goes well for tonight's launch attempt.
I'm doubtful they will be trying anything new on the 2nd stage this time - I think they'll make a small burn after payload separation and send it heliocentric. But who knows - it'll be going super-fast(not far off lunar return velocity) if it returns to Earth, so maybe a good time to test stuff? We'll see soon

29.5deg.inc. due to ASDS position, and also it works fine for TLI for lunar intercept in ~26days. As you say, 28.6deg.inc. is optimal dV-wise, but lots of other constraints on launch time/azimuth/inc. so a few degrees isn't much to worry about.

TESS final orbit at 37deg.inc. sounds right (from the press conference?) but I don't think they mentioned reference frame, so we have to guess. I assumed ecliptic, but maybe I'm wrong. Also mentioned was the 17 x 59 Earth-radii orbit perigee/apogee - but how accurate is that, and is it altitude or radius? Would be nice to have better numbers.....;-)

Your ballute+chute idea sounds plausible - watchout SpaceX don't steal it!

Cheers,
Brian

 

[Marijn]

Hi Brian,
So you were right on them doing a flyback. And launching into a low parking orbit. The reporter said 250x250km. And no giant party balloons or bouncing castle tricks.

Wat do you think about the numbers after the launch? I ran the scenario against the SpaceX webcast a few times. All events up to MECO match up perfectly. But there are more than 30 seconds between the touchdown times of the 1st stage when launching into a 250km orbit, and 45 seconds difference when launching into 250x250km.

It looks to me that the actual 1st stage flips around much more quickly after separation than the simulation in Orbiter and it did deploy its gridfins rather early as well. The whole move seemed very aggresive.

Can you consider these events?

 

[BrianJ]

It looks to me that the actual 1st stage flips around much more quickly after separation than the simulation in Orbiter and it did deploy its gridfins rather early as well. The whole move seemed very aggresive.

Yes, I've noticed that before. I need stronger RCS, I guess. I also think SpaceX ignite the centre engine at low throttle for extra torque before actual boostback attitude is reached.

Also, SpaceX may use a different boostback trajectory to my add-on - I need to go back and look at previous launch video to check 1st stage attitude during boostback burn(where possible). For TESS, the stage looked to be pointed slightly down(lower vert.vel, higher horizontal vel), whereas my add-on points slightly up(higher vert.vel, lower horizontal vel).

Plenty of other factors will make the add-on behave different to real-life.
Bear in mind, I don't really know what I'm doing when it comes to coding and control algorithms, so don't expect too much!

Cheers,
BrianJ

 

[Kyle]

The first stage of F9 started doing "fast flips" for boostback burns starting with CRS-9 in order to utilize less propellant to return back to the launch side/ASDS (a 30 second maneuver for a rocket going ~2 km/s will cover a lot of distance compared to a 5-10 second maneuver). I also think SpaceX does ignite the center engine during this maneuver, too. You can see it happening on the incredible Iridium-4 launch @ the 1:30 mark. I wish SpaceX was as open with their launch profiles as NASA is.

 

[Marijn]

For TESS, the stage looked to be pointed slightly down

For sure it did. The 1st stage seemed to do a clean and simple backward 180 degrees flip without any banking. Starting the flip only moments after separation at about 30 degrees up, it finishes less than 20 seconds later 30 degrees below horizon level. I'am guessing this a bit, but if an aft-facing camera clearly points above the horizon, it's front-facing end must point below the horizon. The SpaceX video shows @6:57 how the aft-facing camera of the 1st stage almost kills rotation having the 2nd stage centered.

So that would mean some thrust of the boostback is pointed down, adding to the entry speed. Only little later they extend the gridfins, inducing drag as early as possible. I wonder what the maximum altitude was of the 1st stage this time. I would say that it was rather low, perhaps not much more than 100-110km.

I am not sure what to make of this. Perhaps they want the landing spot to be as close as possible to the harbor when having the luxury of excess fuel. Cost-wise, that would make sense to me.

Bear in mind, I don't really know what I'm doing when it comes to coding and control algorithms, so don't expect too much!

You're doing a brillant job! While nobody else is doing it better, you are the expert. The F9 add-on pitches up 50 degrees and then banks it's way around. To me, that seems more complicated than doing a half-loop.

 

[Messierhunter]

So that would mean some thrust of the boostback is pointed down, adding to the entry speed.

Correct me if I'm wrong, but this doesn't seem to be necessarily true. If the stage still has positive vertical velocity then thrusting along a vector that will reduce the vertical velocity will ultimately act to reduce the entry speed. A higher apogee equals more vertical velocity at atmospheric entry, reducing vertical velocity therefore reduces the apogee, so as long as the vertical velocity does not start going negative during the boostback burn it should act to minimize entry velocity.

Anecdotally, I use a similar strategy to minimize entry velocity for re-usable rocket I made in KSP. In fact if I don't act quickly to kill the vertical velocity after stage separation, the apogee will be too high and results in catastrophic aerodynamic loads at entry. The trajectory is a very aggressive loft so that I can fly the first stage back to landing and then switch focus to the second stage to insert it into orbit when it hits apogee without having to use any automation mods. It's not directly comparable to SpaceX of course, but I think the principle at work is the same.

 

[Marijn]

Correct me if I'm wrong, but this doesn't seem to be necessarily true.

I think you are correct. It probably does not add to the entry speed. But the nose of the rocket does point below the horizon, so the apoapsis of the 1st stage is lowered during the boostback I would say. Maybe it barely leaves the upper atmosphere. That would explain why they deployed the grid-fins so early.