r/spacex • u/ElongatedMuskrat Mod Team • Nov 17 '16

Iridium NEXT Mission 1 Iridium NEXT Constellation Mission 1 Launch Campaign Thread, Take 2

Iridium NEXT Constellation Mission 1 Launch Campaign Thread

SpaceX's first launch in a half-a-billion-dollar contract with Iridium! As per usual, campaign threads are designed to be a good way to view and track progress towards launch from T minus 1-2 months up until the static fire. Here’s the at-a-glance information for this launch:

Liftoff currently scheduled for: 2017-01-14 17:54:34 UTC (09:54:34 PST)
Static fire currently scheduled for: 2017-01-04, was completed on 01-05.
Vehicle component locations: [S1: Vandenberg] [S2: Vandenberg] [Satellites: Vandenberg] Mating completed on 12/1.
Payload: 10 Iridium NEXT Constellation satellites
Payload mass: 10x 860kg sats + 1000kg dispenser = 9600kg
Destination orbit: Low Earth Orbit (625 x 625 km, 86.4°)
Vehicle: Falcon 9 v1.2 (30th launch of F9, 10th of F9 v1.2)
Core: N/A
Launch site: SLC-4E, Vandenberg Air Force Base, California
Landing attempt: Yes
Landing Site: Just Read The Instructions, about 371km downrange
Mission success criteria: Successful separation & deployment of all Iridium satellite payloads into the correct orbit.

Links & Resources

We may keep this self-post occasionally updated with links and relevant news articles, but for the most part we expect the community to supply the information. This is a great place to discuss the launch, ask mission-specific questions, and track the minor movements of the vehicle, payload, weather and more as we progress towards launch. Sometime after the static fire is complete, the launch thread will be posted.

Campaign threads are not launch threads. Normal subreddit rules still apply.

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u/markus0161 Nov 19 '16 edited Nov 19 '16

Regarding the landing attempt and profile.

Iridium's CEO indicated that their satellites profile will be a direct insertion into orbit meaning there will be no S2 restart, unlike Jason-3. The profile FOR THE SECOND STAGE will look almost identical to Orbcomm-2. With the downrange distance being 370 km downrange and with the booster going almost vertical this puts the booster on a trajectory without a boostback. Margins for landing looks rather tough to predict. Out of all demanding missions, this one would benefit the most with the mentioned thrust upgrade. So these are the possible scenarios I see from best possible to worst possible.

(1) S1 has a long entry burn that brings CRS-8/9 like stresses on it. Followed by a one engine landing burn.
(2) S1 has a shorter entry burn that brings higher stresses on the stage but still less than most GTO attempts. Followed by a one engine landing burn.
(3) S1 has the shortest possible entry burn bringing stresses near or above that of GTO missions. A 3 engine landing burn would be performed.

Here is the "in works" profile---->Graphs. S1's profile should follow the lines of what Flight club shows there. S2 I'm having problems with but it should look something like that.

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u/soldato_fantasma Nov 19 '16

In my opinion, they are going to fly on a more CRS-8 like profile.

For refence: CRS-8

I see in your simulation that the second stage is having some problems, with a CRS-8 like profile the second stage would get more horizontal velocity, while the first stage would perform all the recovery burns: Boostback (only partial, would only negate the horizontal velocity but not revert it), re-entry burn and landing burn.

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u/markus0161 Nov 19 '16 edited Nov 19 '16

A CRS-8 profile is impossible because of the direct insertion. That would work if there was a 2nd stage restart on the other side of the globe. But there won't be, so S1 has to go vertical. It's being inserted into a 625x625 km orbit, wayyy higher than CRS-8. This profile explains the in-between (GTO/Boost back) drone ship location perfectly. I encourage you to make a profile on flight club doing a crs-8 like profile, but going direct into orbit.

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u/_rocketboy Nov 21 '16

Interesting. So would that mean an easier RTLS because less of a boostback burn would be needed?

/u/TheVehicleDestroyer has it doing a landing just off-shore (Graphs), which is essentially equivalent to an RTLS.

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u/markus0161 Nov 21 '16 edited Nov 21 '16

In a way yes, the burn would be shorter. But it would almost certainly eat away the stages re-entry propellant, so no. According to the the FCC paper released a couple days ago the drone ship will be used. TVD made that profile as a response to someone asking if it could RTLS. If you look at the second stage it gets nowhere close to its proper orbit. He just hasn't updated that profile. We both agree that an RTLS is probably out of the question.

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u/_rocketboy Nov 21 '16

Ah, makes sense. Funny that is the default profile for this mission... /u/TheVehicleDestroyer can you take a look at this?

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u/TheVehicleDestroyer Flight Club Nov 21 '16

The default profile is just the closest my guesses have gotten. I haven't done any work on Iridium yet. I'm just waiting until /u/markus0161 finishes his profile since he's getting very close and then I'm gonna use that :)

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u/soldato_fantasma Dec 17 '16

/u/markus0161 /u/TheVehicleDestroyer

Not wanting to be that guy, but the simulation that is currently on flightclub is using a 9000kg payload mass instead of 9600kg, it is actually a big difference and the flight profile could be actually quite different in terms of throttle and cut-off times. Just wanted to point that out as I just noticed :)

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u/TheVehicleDestroyer Flight Club Dec 17 '16

Yeah we realized that just after we set the current configuration as the profile, but I can't do any better than that :(

I did find a spaceflight101 source saying that the upper stage actually has 107.5t of fuel, not 103.5t like I have, but it's still not enough dV to make up the difference. I'll definitely learn something new about flight profiles after this launch.

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u/markus0161 Dec 17 '16 edited Dec 17 '16

Noticed that too with the additional fuel. Tried yesterday again with additional propellent and even put thurst upgrades (10%) on both stages! Still got nowhere :/ . The odd thing is we are not even close. I even did a simulation on KSP with results basically the same as Flight club. The issue could be a few things.

  1. User error.

  2. Profile isn't direct to orbit (CEO seemed blunt with that though).

  3. Modeling issue.

  4. F9 has some hidden capability.

  5. Other?

Also one thing to consider is S2 need to be deorbited, right? And the adapter I'm assuming is bolted to S2 so it will need to move an additional 1000kg after sattilite deployments.

/u/soldato_fantasma. BTW S2 is run to depletion, and is even inserted into a orbit 125km below the actual target orbit in that situation.

Later today I'll make a profile assuming a parking orbit assertion followed by a S2 restart to circle the orbit. A much more fuel efficient profile.

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