MRO, MSL, Juno, MAVEN, O-Rex, PNH, etc had windows of 30 minutes or more and flew the same first stage trajectory.
MSL had instantaneous windows, 5 minutes apart, all the way through the almost 2 hour launch window. Are you saying all of these had the same azimuth? If so, why? It's definitely giving up performance. What's the corresponding benefit?
A heck of a lot less range safety analyses/products, telemetry products, analyses, etc.
MSL had instantaneous windows, 5 minutes apart, all the way through the almost 2 hour launch window. Are you saying all of these had the same azimuth? If so, why? It's definitely giving up performance. What's the corresponding benefit?
They were not instantaneous windows. It had one continuous window at the same azimuth. They just scheduled launch attempts every 5 minutes. This was for down range tracking and spacecraft acquisition.
The flight profile from liftoff to Centaur MECO-1 were the same for all times and days.
MSL had instantaneous windows, 5 minutes apart, all the way through the almost 2 hour launch window. Are you saying all of these had the same azimuth? If so, why? It's definitely giving up performance. What's the corresponding benefit?
They were not instantaneous windows. It had one continuous window at the same azimuth. They just scheduled launch attempts every 5 minutes. This was for down range tracking and spacecraft acquisition.
From
the MAVEN launch"For MAVEN, we've got a two-hour launch opportunity every day," said Jim Sponnick, ULA's vice president of Atlas and Delta programs. "And within those two hours, we have an opportunity to launch once every five minutes. It's those opportunities each day over the launch window make up those 1,000 trajectories. It's fairly consistent with how we have designed, developed and validated trajectories and mission designs for previous missions to Mars."
So you have one opportunity, each five minutes, each with its own trajectory. If you miss one, you wait for the next. That's the very definition of a sequence of instantaneous launch windows. Now if you want to claim it's due to tracking, and not the rocket, that's one thing. But for whatever reason, ULA implemented a sequence of instantaneous launch windows.
The flight profile from liftoff to Centaur MECO-1 were the same for all times and days.
So you are saying the first stage has a continuous window, so you can launch the first stage at any time you want, and it will work perfectly. I'd agree with that. Unfortunately, if you don't pick a time that is also compatible with the second stage working correctly, your mission will fail. Strangely enough, customers want launch windows where everything will work - first stage, second stage, tracking, sunlight, etc. So the mission launch window is the AND of all these constraints. In this case, it's a sequence of instantaneous windows.
So you are saying the first stage has a continuous window, so you can launch the first stage at any time you want, and it will work perfectly. I'd agree with that. Unfortunately, if you don't pick a time that is also compatible with the second stage working correctly,
And the second stage has continuous window. It would work perfectly for anytime within the window. There is only one software load for the whole window
So you are saying the first stage has a continuous window, so you can launch the first stage at any time you want, and it will work perfectly. I'd agree with that. Unfortunately, if you don't pick a time that is also compatible with the second stage working correctly,
And the second stage has continuous window. It would work perfectly for anytime within the window. There is only one software load for the whole window
So a single software load can include a bunch of trajectories, and the avionics, or the ground, picks one based on the launch time (from previous article):
Based on the rotation of Earth and the alignment of planets, the trajectory to Mars changes throughout the launch window. So engineers pre-developed 1,000 trajectory programs to load into the Atlas 5's guidance computer in case the launch delays into the window.
So if each trajectory has its own launch window, and you can load enough individual trajectories to tile the entire daily launch window, then you could in theory launch at any time. The constraint on the avionics is the ability to load, hold, and pick from enough trajectories. This seems pretty straightforward for any modern avionics, but could well explain why Delta has not pursued this strategy.
Continuous coverage seems like more work than required, since you only really need trajectories that work at the times permitted by other constraints. On the other hand, presumably each of the trajectories is generated by the usual process, which will give a window as one of its outputs (or take it as a constraint). If those windows are big enough (>= 5 minutes in this case) then it's no extra work to get continuous converage.
With 1000 different trajectories, I can see why ULA would hold as much as possible of the flight the same. That way they don't need 1000 different predicts to send to the tracking stations. The disadvantage would be that performance drops off more quickly from the center of the window, so this is probably why the Atlas launch windows are not as long as the more than 2.5 hour Apollo launch windows. Such long windows would require changing the launch azimuth to avoid excessive losses. But the shorter windows seem plenty good enough - i can't recall any planetary mission lately that was in danger of missing the launch window, but might have made it if the daily windows were longer.
The disadvantage would be that performance drops off more quickly from the center of the window, so this is probably why the Atlas launch windows are not as long as the more than 2.5 hour Apollo launch windows.
Lunar trajectories are not to be compared to other planetary windows.
The disadvantage would be that performance drops off more quickly from the center of the window, so this is probably why the Atlas launch windows are not as long as the more than 2.5 hour Apollo launch windows.
Lunar trajectories are not to be compared to other planetary windows.
Lunar and planetary windows should be pretty similar. In both cases, the orbital mechanics dictate an orbit with the perigee near Earth and an extremely high apogee. So the optimal injection spot is almost directly opposite the desired departure direction. In a two hour window, this spot moves by about 30 degrees in longitude.
A planet is pretty much fixed in place on this time scale, but the moon is moving. Assuming it goes around in 28 days, it will move about 1 degree in a two hour window. So instead of 30 degrees, the optimal spot moves only 29. So a moon window will be about 3% longer for the same amount of allowed mis-alignment.
Bumping this old thread, because I believe we've just seen Falcon 9 fully demonstrate yaw steering capability. The SAOCOM 1B launch involved dog leg maneuvers in both first and second stages, followed by an RLTS landing. Does this mean that, given sufficient prop margins, that some instantaneous launch windows could be expanded?
Bumping this old thread, because I believe we've just seen Falcon 9 fully demonstrate yaw steering capability. The SAOCOM 1B launch involved dog leg maneuvers in both first and second stages, followed by an RLTS landing. Does this mean that, given sufficient prop margins, that some instantaneous launch windows could be expanded?
Given margin, yes. But I know SAOCOM was a light payload. Anyone have full numbers for the payload? And the losses incurred compared to other RTLS launches?
Does this mean that, given sufficient prop margins, that some instantaneous launch windows could be expanded?
For Falcon 9, recycle time would be limited by propellant temperature due to the use of subcooling. Unless the window is sufficiently long to allow tanks to be drained and refilled, or clearing the hold condition so rapid that it can be done before the propellants warm, a short window gained through RAAN/yaw steering is of not practical use 'just' for expanding the launch window.
During SAOCOM 1B launch coverage, the SpaceX commentator put it very understandably. He stated that while this launch had a 10-minute launch window, once prop loading began, the launch window became instantaneous at the designated T-0 time, since the props would warm too much even during a short hold to delay beyond the exact launch time.
So, launch of a Falcon 9 has to happen at an exact interval after prop loading begins. Once you start loading the tanks, you've committed to either launching exactly on time, or not launching at all. Such is the world of subcooled propellants...
They can cycle the propellants for a second attempt in their four hour launch windows for GTO launches, but obviously that is limited to payloads that don't care too much about time of day.
I don't think they can recycle Falcon Heavy, only delay prop loading if they have a window. I was there for Arabsat-6A and on the second attempt, I'm pretty sure they said it would be a scrub if there was any problems after commit to prop load, although that was only a ~2hr window. I'm not sure why Jim is dancing around this, unless Psyche itself has an instantaneous launch window...?
I already stated it does. Like for ISS missions, Falcon can only do instantaneous windows for planetary missions. It is a function of its avionics. It can’t do RAAN steering.
They can cycle the propellants for a second attempt in their four hour launch windows for GTO launches, but obviously that is limited to payloads that don't care too much about time of day.
I don't think they can recycle Falcon Heavy, only delay prop loading if they have a window. I was there for Arabsat-6A and on the second attempt, I'm pretty sure they said it would be a scrub if there was any problems after commit to prop load, although that was only a ~2hr window. I'm not sure why Jim is dancing around this, unless Psyche itself has an instantaneous launch window...?
I already stated it does. Like for ISS missions, Falcon can only do instantaneous windows for planetary missions. It is a function of its avionics. It can’t do RAAN steering.
How does RAAN steering differ from the maneuvers needed to do a dogleg as Falcon 9 has done on occasion? Is it because the dogleg is planned in advance for a particular launch time, while RAAN steering varies in real time as the launch time slips?
They can cycle the propellants for a second attempt in their four hour launch windows for GTO launches, but obviously that is limited to payloads that don't care too much about time of day.
I don't think they can recycle Falcon Heavy, only delay prop loading if they have a window. I was there for Arabsat-6A and on the second attempt, I'm pretty sure they said it would be a scrub if there was any problems after commit to prop load, although that was only a ~2hr window. I'm not sure why Jim is dancing around this, unless Psyche itself has an instantaneous launch window...?
I already stated it does. Like for ISS missions, Falcon can only do instantaneous windows for planetary missions. It is a function of its avionics. It can’t do RAAN steering.
How does RAAN steering differ from the maneuvers needed to do a dogleg as Falcon 9 has done on occasion? Is it because the dogleg is planned in advance for a particular launch time, while RAAN steering varies in real time as the launch time slips?
yes
In that case, we would expect it's just a SMoP. SMoP fills real programmers with dread. A manager says it's a "Small Matter of Programming". The guys who are expected to implement it know they are now in trouble.
They can cycle the propellants for a second attempt in their four hour launch windows for GTO launches, but obviously that is limited to payloads that don't care too much about time of day.
I don't think they can recycle Falcon Heavy, only delay prop loading if they have a window. I was there for Arabsat-6A and on the second attempt, I'm pretty sure they said it would be a scrub if there was any problems after commit to prop load, although that was only a ~2hr window. I'm not sure why Jim is dancing around this, unless Psyche itself has an instantaneous launch window...?
I already stated it does. Like for ISS missions, Falcon can only do instantaneous windows for planetary missions. It is a function of its avionics. It can’t do RAAN steering.
How does RAAN steering differ from the maneuvers needed to do a dogleg as Falcon 9 has done on occasion? Is it because the dogleg is planned in advance for a particular launch time, while RAAN steering varies in real time as the launch time slips?
yes
In that case, we would expect it's just a SMoP. SMoP fills real programmers with dread. A manager says it's a "Small Matter of Programming". The guys who are expected to implement it know they are now in trouble.
Right. You could just pre-compute thousands of trajectories in one second intervals for the whole window. If it’s worth having the capability, SpaceX could easily do it.
They can cycle the propellants for a second attempt in their four hour launch windows for GTO launches, but obviously that is limited to payloads that don't care too much about time of day.
I don't think they can recycle Falcon Heavy, only delay prop loading if they have a window. I was there for Arabsat-6A and on the second attempt, I'm pretty sure they said it would be a scrub if there was any problems after commit to prop load, although that was only a ~2hr window. I'm not sure why Jim is dancing around this, unless Psyche itself has an instantaneous launch window...?
I already stated it does. Like for ISS missions, Falcon can only do instantaneous windows for planetary missions. It is a function of its avionics. It can’t do RAAN steering.
How does RAAN steering differ from the maneuvers needed to do a dogleg as Falcon 9 has done on occasion? Is it because the dogleg is planned in advance for a particular launch time, while RAAN steering varies in real time as the launch time slips?
yes
In that case, we would expect it's just a SMoP. SMoP fills real programmers with dread. A manager says it's a "Small Matter of Programming". The guys who are expected to implement it know they are now in trouble.
Right. You could just pre-compute thousands of trajectories in one second intervals for the whole window. If it’s worth having the capability, SpaceX could easily do it.
Your statement is an excellent example of SMoP.
Absolutely. The programmers would hate whoever made them do it. “Just solve it in software” LOL. They hate that.
Right. You could just pre-compute thousands of trajectories in one second intervals for the whole window. If it’s worth having the capability, SpaceX could easily do it.
Wrong on both points. 7200 trajectories for a two hour window is too much to manage.
