SpaceX Falcon 9 / Dragon 2 : SpX-DM1 : March 2, 2019 : DISCUSSION

[Alexphysics]

In answer to a question about the drone ship landing, Hans said they were reserving performance and flying a lofted trajectory.

The opposite, this flight is not flying on a lofted trajectory so that and the reserve of performance means no land landing. A lofted trajectory is more harder for g loads on entry during an in-flight abort. Cargo doesn't care about that but crew will care. On future missions they could take out part of that performance reserve and use it to land the first stage back on land.

[octavo]

In answer to a question about the drone ship landing, Hans said they were reserving performance and flying a lofted trajectory.

The opposite, this flight is not flying on a lofted trajectory so that and the reserve of performance means no land landing. A lofted trajectory is more harder for g loads on entry during an in-flight abort. Cargo doesn't care about that but crew will care. On future missions they could take out part of that performance reserve and use it to land the first stage back on land.

I know what a lofted trajectory is and why they're flying it. The point is he said they can do an lz landing even with the lofted trajectory and the drone shop is there not just because of the trajectory, but because they want to reserve performance. Which implies an abundance of caution to me and following from that, more prop in the event of success.

[ZChris13]

I know what a lofted trajectory is and why they're flying it.

you have it backwards, SpaceX are not flying a lofted trajectory on DM-1, they are throwing the upper stage much lower and faster than the typical lofted trajectories they use for cargo

[su27k]

In answer to a question about the drone ship landing, Hans said they were reserving performance and flying a lofted trajectory. He added that they may return to lz landings for future dragon 2 flights.

To me this implies that the booster will be landing with a lot of unused propellant if the flight goes well.

It would make much more sense to just burn the reserved propellant during ascend to give extra delta-v to the upper stage and spacecraft.

[Alexphysics]

In answer to a question about the drone ship landing, Hans said they were reserving performance and flying a lofted trajectory.

The opposite, this flight is not flying on a lofted trajectory so that and the reserve of performance means no land landing. A lofted trajectory is more harder for g loads on entry during an in-flight abort. Cargo doesn't care about that but crew will care. On future missions they could take out part of that performance reserve and use it to land the first stage back on land.

I know what a lofted trajectory is and why they're flying it. The point is he said they can do an lz landing even with the lofted trajectory and the drone shop is there not just because of the trajectory, but because they want to reserve performance. Which implies an abundance of caution to me and following from that, more prop in the event of success.

I told you it is the opposite they are NOT flying a lofted trajectory because of the high g's at reentry. ADDED to that there's also some reserve of performance they're doing to ensure Dragon will get into orbit. He said that on future missions they could probably make it go back to land. The most probable explanation for that is that they still have some room for optimization of the trajectory and wihout that reserve of performance they may be able to land the stage back to land in the future.

[rsnellenberger]

Gerstenmaier mentioned a need/desire for a 24 hour docking time due to thermal constraints (presumably on Dragon). Since this is the first use of an IDA on-orbit, I’m curious what the contingency plans are for dealing with any issues that arise - how many attempts are possible, amount of “loiter time” available to diagnose/work issues, etc.

Original requirement was for docking up to 24hr after launch, with one retry within one orbit after that (see CCT-REQ-1130-146207-DRAFT-001-001 here).

No idea if that has changed since original requirements were issued.  If not, Gerst was likely reiterating the requirement.  Whether Dragon-2 can provide additional loiter time or docking retries is anyone's guess.

My main interest, to be honest, is in the contingency options (if any) that have been developed in the event of an IDA issue.

[Targeteer]

The Russians obviously have a presence at the FRR because they voiced a concern and a cast a negative vote.  Does NASA have a presence on the Russian State Commission that approves their launches to the Station?

[ZachS09]

Since the drone ship will be nearly 500 kilometers away from KSC, what burn profile will the booster use?

The 2-burn profile used on GTO missions, or the 3-burn profile as seen in the SpaceX CRS-8 mission?

[Orbiter]

Since the drone ship will be nearly 500 kilometers away from KSC, what burn profile will the booster use?

The 2-burn profile used on GTO missions, or the 3-burn profile as seen in the SpaceX CRS-8 mission?

Almost certainly a 3-burn profile.

[John Santos]

What makes sense to me is they would plan to use all the reserve propellant during the first stage burn.  This would leave a lot of extra performance on the table beyond what the 2nd stage will need to provide.  But if they lose an engine during 1st stage, they could use that 2nd stage excess to complete the mission.  To maximize this contingency, they will land on the drone ship way down range, rather than doing a boost-back and landing at LZ-1.
The reason for this is they would hate to lose the mission (but not necessarily the Dragon, which I'm pretty sure has normal abort capabilities) and have to do the whole thing all over again just because an M1D died.  (Which, IIRC, has only happened once, but that was during the 1st cargo Dragon launch.)

The primary point of this mission is to test Dragon 2 in orbit, not to test the F9, and if they failed to be able to attempt that due to no failing on the Dragon's part, it would be a wasted opportunity.

Someone asked if they would be doing 2 or 3 landing burns.  I think the 1st burn is the boost-back burn, which kills all the down-range velocity and sends the F9 back towards the launch site for an LZ landing.  Since they aren't doing that, I'm sure there won't be a boost back burn, just the re-entry and landing burns.  Two, not three.

I think the 1-3-1 thing pertains to just the landing burn, where they ignite the center engine, then two outer engines, then shutdown the two outer engines just before landing.  I think this uses less fuel than a single-engine landing burn.

We'll see in a week, if the press materials they usually release a few days before the launch don't cover all this.

BTW, one thing I'm curious about is the approach and docking procedures. On the first flights of most or all of the cargo vessels (ATV, HTV, Cygnus and Cargo Dragon), they did several "practice" approaches with holds and sometimes simulated emergency back-offs as they tested the approach.  Are they planning to do that kind of testing this time, or just come in and dock?  (Especially because they will be docking rather than just station-keeping close enough to be grabbed and berthed by the SSRMS.  The only previous cargo vessels to dock rather than berth were Progress and ATV, which used the Progress automated docking hardware and software, IIRC.)

[woods170]

What makes sense to me is they would plan to use all the reserve propellant during the first stage burn.  This would leave a lot of extra performance on the table beyond what the 2nd stage will need to provide.  But if they lose an engine during 1st stage, they could use that 2nd stage excess to complete the mission.  To maximize this contingency, they will land on the drone ship way down range, rather than doing a boost-back and landing at LZ-1.
The reason for this is they would hate to lose the mission (but not necessarily the Dragon, which I'm pretty sure has normal abort capabilities) and have to do the whole thing all over again just because an M1D died.  (Which, IIRC, has only happened once, but that was during the 1st cargo Dragon launch.)

<snip>

Emphasis mine.

On the CRS-1 mission the launch vehicle (Falcon 9 v1.0) lost an engine during ascent. That was not an M1D, but  an earlier M1C. That's because Falcon 9 v1.0 flew with M1C's only. M1D's started flying with the introduction of F9 v1.1.

SpaceX, to this date, has never suffered an inflight-failure of an M1D engine.

[Alexphysics]

Someone asked if they would be doing 2 or 3 landing burns.  I think the 1st burn is the boost-back burn, which kills all the down-range velocity and sends the F9 back towards the launch site for an LZ landing.  Since they aren't doing that, I'm sure there won't be a boost back burn, just the re-entry and landing burns.  Two, not three.

I think the 1-3-1 thing pertains to just the landing burn, where they ignite the center engine, then two outer engines, then shutdown the two outer engines just before landing.  I think this uses less fuel than a single-engine landing burn.

They do boostbacks for droneship landings too, those just cancel horizontal velocity and not reverse it to land, but they perform those too. The 1-3-1 profile is the usual one for boostback burn and reentry burn. Landing burn could be just 1 or 1-3-1 depending on their needs and they have done both on multiple and different landing scenarios.

[Lars-J]

Someone asked if they would be doing 2 or 3 landing burns.  I think the 1st burn is the boost-back burn, which kills all the down-range velocity and sends the F9 back towards the launch site for an LZ landing.  Since they aren't doing that, I'm sure there won't be a boost back burn, just the re-entry and landing burns.  Two, not three.

I think the 1-3-1 thing pertains to just the landing burn, where they ignite the center engine, then two outer engines, then shutdown the two outer engines just before landing.  I think this uses less fuel than a single-engine landing burn.

They do boostbacks for droneship landings too, those just cancel horizontal velocity and not reverse it to land, but they perform those too. The 1-3-1 profile is the usual one for boostback burn and reentry burn. Landing burn could be just 1 or 1-3-1 depending on their needs and they have done both on multiple and different landing scenarios.

Maybe you mean that those burns adjust the horizontal velocity, because they certainly don't outright cancel the horizontal velocity. That would make them fall straight down, which would be unnecessary and a waste of propellant.

The burns done right after stage separation for barge landings are more accurately described as aiming burns, to aim the ballistic impact point near the barge.

[Alexphysics]

Someone asked if they would be doing 2 or 3 landing burns.  I think the 1st burn is the boost-back burn, which kills all the down-range velocity and sends the F9 back towards the launch site for an LZ landing.  Since they aren't doing that, I'm sure there won't be a boost back burn, just the re-entry and landing burns.  Two, not three.

I think the 1-3-1 thing pertains to just the landing burn, where they ignite the center engine, then two outer engines, then shutdown the two outer engines just before landing.  I think this uses less fuel than a single-engine landing burn.

They do boostbacks for droneship landings too, those just cancel horizontal velocity and not reverse it to land, but they perform those too. The 1-3-1 profile is the usual one for boostback burn and reentry burn. Landing burn could be just 1 or 1-3-1 depending on their needs and they have done both on multiple and different landing scenarios.

Maybe you mean that those burns adjust the horizontal velocity, because they certainly don't outright cancel the horizontal velocity. That would make them fall straight down, which would be unnecessary and a waste of propellant.

The burns done right after stage separation for barge landings are more accurately described as aiming burns, to aim the ballistic impact point near the barge.

Would you prefer "reduce by a lot" the horizontal velocity?

[Citabria]

Would you prefer "reduce by a lot" the horizontal velocity?

Or, you could use numbers. Just a thought.

[Lars-J]

They do boostbacks for droneship landings too, those just cancel horizontal velocity and not reverse it to land, but they perform those too. The 1-3-1 profile is the usual one for boostback burn and reentry burn. Landing burn could be just 1 or 1-3-1 depending on their needs and they have done both on multiple and different landing scenarios.

Maybe you mean that those burns adjust the horizontal velocity, because they certainly don't outright cancel the horizontal velocity. That would make them fall straight down, which would be unnecessary and a waste of propellant.

The burns done right after stage separation for barge landings are more accurately described as aiming burns, to aim the ballistic impact point near the barge.

Would you prefer "reduce by a lot" the horizontal velocity?

You are assuming it is reducing it. To aim to the landing site, you could hypothetically have a boost-forward or boost sideways. But most of the time it will just reduce it... And not necessarily by a lot (again, wastes propellant), it just depends where the barge is placed which is probably calculated by how much margin they think they will have. SpaceX would prefer to have the barge closer to land for faster recovery, but it also increases the recovery propellant needs. So it is a trade-off.

[Alexphysics]

Would you prefer "reduce by a lot" the horizontal velocity?

Or, you could use numbers. Just a thought.

Then I would need different numbers for different missions and we wouldn't finish this conversation

[FutureSpaceTourist]

Not sure where to post this; NASA has released a hi-res version of the Dragon 2 docking render from SpaceX.

[wardy89]

Launch Hazard Areas for SpaceX Mission 1377 DM1 according NOTMAR message, valid for Saturday 02 Mar 07:40-08:20 UTC - alternate Tuesday 05 Mar 06:30-07:10 UTC.
Marked droneship landing for B1051.
Next two unusual Hazard Areas further in the flight path located east of Newfoundland island and west of Ireland.
Appropriate NOTAMs would be included later.

Could the the Hazard areas further down range relate to Launch abort scenarios further into flight but before orbital velocity? with potential splash down areas close to land for fast recovery?

[Comga]

Launch Hazard Areas for SpaceX Mission 1377 DM1 according NOTMAR message, valid for Saturday 02 Mar 07:40-08:20 UTC - alternate Tuesday 05 Mar 06:30-07:10 UTC.
Marked droneship landing for B1051.
Next two unusual Hazard Areas further in the flight path located east of Newfoundland island and west of Ireland.
Appropriate NOTAMs would be included later.

The location of the ASDS is beyond the middle of the second hazard zone, which is presumably for the first stage reentering ballisticly
Does this say that there will be very little or no velocity scrubbed after staging?