Author Topic: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 22, 2018 - DISCUSSION  (Read 68290 times)

Offline Ultrafamicom

  • Member
  • Posts: 26
  • Liked: 7
  • Likes Given: 13
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #80 on: 04/10/2018 02:13 PM »
Please note the rather significant difference in orbital altitude between GRACE-FO and the Iridium sats and than remember that neither GRACE-FO, nor the Iridium sats have circularisation capabilities.

I see what Ultrafamicom is getting at, but if you deploy the Iridium satellites first, you then require the same plane change (admittedly of less mass), combined with the additional ∆V of a reduction in perigee, a circularisation at 490kms before deployment of the GRACE-FO satellites, and ultimately a de-orbit burn. So, four S2 burns, and probably a higher ∆V requirement.

Indeed. And although an F9 S2 is quite capable it does make sense to do things as efficiently as possible. Which precludes dropping off the Iridium sats first.

For efficiency it is preferred to drop off the Iridium sats first.
While plane change cost near 400m/s delta-v, launching to 625km costs only 70m/s more than 490km(may be a little more for direct ascension). So the options are 1. haul 6t to GRACE-FO orbit, release 1.2t, burn 400m/s with 4.8t  payload, deorbit(+35m/s for higher apogee) 2. haul 6t to GRACE-FO orbit plus 70m/s, release 4.3t, burn 400m/s  with 1.7t  payload, deorbit. The latter one seems to be better.

A real concern may be the structures, thanks Semmel for pointing out.
« Last Edit: 04/10/2018 02:15 PM by Ultrafamicom »

Offline Comga

  • Senior Member
  • *****
  • Posts: 4152
  • Liked: 1426
  • Likes Given: 1178
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #81 on: 04/10/2018 02:52 PM »
I'm predicting that the second stage will directly insert itself into the GRACE-FO orbit (490 km, inclined 89 degrees) before the second burn increases the apogee and lowers the inclination while the third burn circularizes the Iridium-NEXT orbit (625 km, inclined 86.66 degrees).

"Discussion without numerical analysis is just opinion."
There is always an optimum distribution of the plane change between the two burns.
It generally goes as the ratio of the velocities.
Given that these orbits are not significantly different in velocity, like between the perigee and apogee of a GTO, the plane change will be nearly evenly split, with slightly more than half at the slower upper orbit.
Of course, given that this post is also without numerical analysis, it is also just an opinion, but we can say that "the exercise is left to the reader."  :)
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline envy887

  • Senior Member
  • *****
  • Posts: 3980
  • Liked: 2053
  • Likes Given: 1230
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #82 on: 04/10/2018 04:33 PM »
Please note the rather significant difference in orbital altitude between GRACE-FO and the Iridium sats and than remember that neither GRACE-FO, nor the Iridium sats have circularisation capabilities.

I see what Ultrafamicom is getting at, but if you deploy the Iridium satellites first, you then require the same plane change (admittedly of less mass), combined with the additional ∆V of a reduction in perigee, a circularisation at 490kms before deployment of the GRACE-FO satellites, and ultimately a de-orbit burn. So, four S2 burns, and probably a higher ∆V requirement.

Indeed. And although an F9 S2 is quite capable it does make sense to do things as efficiently as possible. Which precludes dropping off the Iridium sats first.

Also, for structural reasons, it makes sense to put the heavier sats below the light sats. Otherwise the payload would be quite top heavy in comparison..

Aren't the Iridium satellites ejected to the side? Why couldn't they put the Iridiums on the bottom and still eject them first?

Offline kevin-rf

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8643
  • Overlooking the path Mary's little Lamb took..
  • Liked: 1112
  • Likes Given: 242
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #83 on: 04/10/2018 07:02 PM »
Also, for structural reasons, it makes sense to put the heavier sats below the light sats. Otherwise the payload would be quite top heavy in comparison..

Huh? From a rocket control perspective, the farther forward you move the rocket's center of mass (Top Heavy), the easier the control problem becomes. That's why the LOX tank is usually above the kero tank in most rocket first stage designs. The only real exception is some LH upper-stages where it is reversed due to it being more mass efficient to run LH piping around and through the much smaller LOX tank.
If you're happy and you know it,
It's your med's!

Offline envy887

  • Senior Member
  • *****
  • Posts: 3980
  • Liked: 2053
  • Likes Given: 1230
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #84 on: 04/10/2018 08:28 PM »
Also, for structural reasons, it makes sense to put the heavier sats below the light sats. Otherwise the payload would be quite top heavy in comparison..

Huh? From a rocket control perspective, the farther forward you move the rocket's center of mass (Top Heavy), the easier the control problem becomes. That's why the LOX tank is usually above the kero tank in most rocket first stage designs. The only real exception is some LH upper-stages where it is reversed due to it being more mass efficient to run LH piping around and through the much smaller LOX tank.

Control and structural concerns are separate. If the Iridiums are on top, the GRACE-FO dispenser has to support their 4800 kg mass under 6 g acceleration (plus vibration, out of axis loads, etc.).

Online vaporcobra

  • Full Member
  • ****
  • Posts: 981
  • Tacoma, WA
  • Liked: 1616
  • Likes Given: 2108
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #85 on: 04/10/2018 08:40 PM »
We've known this for awhile. GRACE-FO on the top dispenser.

GRACE-FO on the top dispenser, Iridium on the bottom dispenser.

Quote
"Following next month’s launch, our cadence with SpaceX should move more rapidly as launch frequency is planned to increase to approximately one launch every five to six weeks or so. In fact, our sixth launch is currently scheduled for a quick turnaround at the end of April, that will be a rideshare with the JPL German Grace satellites in which we’ll utilize half of the payload to launch five Iridium NEXT satellites alongside the two Grace satellites which will be mounted on the dispenser above ours."

Online Targeteer

  • Senior Member
  • *****
  • Posts: 3746
  • near hangar 18
  • Liked: 892
  • Likes Given: 450
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #86 on: 04/10/2018 09:06 PM »
April 10, 2018
MEDIA ADVISORY M18-057
NASA Invites Media to Launch of GRACE Follow-On Spacecraft
 

The two satellites that make up NASA’s Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, launching May 19, 2018, will monitor changes in ice sheets and glaciers, underground water storage and sea level, providing a unique view of Earth’s climate that has far-reaching benefits.

Credits: NASA

Media accreditation now is open to cover the launch of NASA’s Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission – twin satellites that constitute the agency’s latest Earth-observing mission.

GRACE-FO will continue the task of the original GRACE mission, providing critical measurements that will be used with other data to monitor the movement of water masses across the planet and mass changes within the Earth itself. Monitoring changes in ice sheets and glaciers, underground water storage and sea level provides a unique view of Earth’s climate and has far-reaching benefits.

GRACE-FO will launch as part of a commercial rideshare mission with five Iridium Communications Inc. satellites aboard a SpaceX Falcon 9 rocket. The Iridium-6/GRACE-FO launch is scheduled for no earlier than 1:03 p.m. PDT (4:03 p.m. EDT) May 19 from Vandenberg Air Force Base in California.

Media who are interested in covering the launch at Vandenberg can apply by emailing [email protected]

Media who are foreign nationals or green card holders must complete an online application and provide a photocopy of their passport to [email protected] no later than 2 p.m. PDT Monday, April 16. Media who are U.S. citizens must apply online no later than 2 p.m. Sunday, May 13.

Vandenberg Air Force Base security will have final authority to decide which media are credentialed to cover launches, and submitting the request by the deadline does not guarantee approval.

NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the GRACE-FO mission for the agency’s Science Mission Directorate in Washington, under the direction of the Earth Systematic Missions Program Office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The spacecraft were built by Airbus Defence and Space in Friedrichshafen, Germany, under subcontract to JPL. The GFZ German Research Centre for Geosciences contracted GRACE-FO launch services from Iridium. GFZ has subcontracted mission operations to the German Aerospace Center (DLR), which operates the German Space Operations Center in Oberpfaffenhofen, Germany.

Additional details on the mission and prelaunch media activities will be announced closer to the launch date.

For more information on GRACE-FO, visit:

https://www.nasa.gov/gracefo
Best quote heard during an inspection, "I was unaware that I was the only one who was aware."

Offline Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 15361
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 4672
  • Likes Given: 604
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #87 on: 04/11/2018 06:08 AM »
I'm predicting that the second stage will directly insert itself into the GRACE-FO orbit (490 km, inclined 89 degrees) before the second burn increases the apogee and lowers the inclination while the third burn circularizes the Iridium-NEXT orbit (625 km, inclined 86.66 degrees).

Actually, you want to split the plane change at both perigee and apogee to get the best performance. This saves you 57 m/s! Attached is the program I used to calculated this.

Enter initial perigee height (km): 490
Enter initial apogee height (km): 490
Enter required inclination change (deg): 2.34
Enter final orbit height (km): 625

theta1 =  2.34 deg, dv1 =  339.4 m/s
theta2 =  0.00 deg, dv2 =  144.7 m/s
dv =  484.0 m/s

theta1 =  1.26 deg, dv1 =  218.4 m/s
theta2 =  1.08 deg, dv2 =  208.7 m/s
dv =  427.1 m/s
« Last Edit: 04/11/2018 06:18 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Online vaporcobra

  • Full Member
  • ****
  • Posts: 981
  • Tacoma, WA
  • Liked: 1616
  • Likes Given: 2108
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #88 on: 04/16/2018 03:23 AM »
Brian Webb (Vandy's Launch Alert dude) may have just suggested that Iridium-6 and Iridium-7 have swapped spots. I'm checking to see if it was a mistake, but it seems unlikely given that he uses the correct satellite numbers for 6-8.

Offline cppetrie

  • Full Member
  • ****
  • Posts: 591
  • Liked: 338
  • Likes Given: 3
Re: SpaceX F9 : Iridium NEXT 6 with GRACE-FO : NET May 19, 2018
« Reply #89 on: 04/16/2018 05:44 AM »
Brian Webb (Vandy's Launch Alert dude) may have just suggested that Iridium-6 and Iridium-7 have swapped spots. I'm checking to see if it was a mistake, but it seems unlikely given that he uses the correct satellite numbers for 6-8.
Seems like typo. He has a second GRACE-FO pair going with 10 Iridium sats in August. That’s not even possible let alone not what the plan is.

Offline ZachS09

Quote
May 19 2018 on a new Falcon 9

Do we not have confirmation from Matt Desch that this will be flight-proven?

It was said that Core B1043 would be used on the Iridium-NEXT F6 & GRACE-FO mission.

And obviously, because it's a Block 4 booster, it will be expended with a considerable amount of fuel left for EDL tests.
« Last Edit: 04/25/2018 03:50 PM by ZachS09 »
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Offline gongora

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 3245
  • US
  • Liked: 2627
  • Likes Given: 1576
Tweet from Matt Desch:
Quote
The first few satellites went through full vacuum and thermal (and acoustic etc) tests to validate the design (and assembly processes).  Subsequent vehicles only go through thermal cycling to validate assembly workmanship.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2048
  • Fife
  • Liked: 1006
  • Likes Given: 1123
Some pre-launch information on GRACE-FO.
I don't think there is anything that has not been well covered before.


Offline andrewsdanj

  • Member
  • Posts: 93
  • Liked: 52
  • Likes Given: 33
From the update thread we apparently have two 'second stage' entry areas active 11 minutes apart. Have we seen this before? Are we about to see some more aggressive/active S2 entry testing?

Offline SciNews

  • Full Member
  • *
  • Posts: 132
  • Romania
  • Liked: 137
  • Likes Given: 4
Some pre-launch information on GRACE-FO.
I don't think there is anything that has not been well covered before.
Edited version of the video with added illustration of GRACE-FO components, short time-lapse of installation and a picture of the twin satellites.

Offline ZachS09

Remind me if this question was answered already:

Does GRACE-FO use the same dispenser as the one for Iridium-NEXT? If not, then the top dispenser should be lighter than 500 kilograms.
« Last Edit: 05/16/2018 02:58 PM by ZachS09 »
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Offline gongora

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 3245
  • US
  • Liked: 2627
  • Likes Given: 1576
Remind me if this question was answered already:

Does GRACE-FO use the same dispenser as the one for Iridium-NEXT? If not, then the top dispenser should be lighter than 500 kilograms.

Completely different. (Airbus made the GRACE-FO dispenser)
« Last Edit: 05/16/2018 03:02 PM by gongora »

Offline Heinrich

  • Full Member
  • *
  • Posts: 124
  • Liked: 5
  • Likes Given: 101
From the update thread we apparently have two 'second stage' entry areas active 11 minutes apart. Have we seen this before? Are we about to see some more aggressive/active S2 entry testing?
Brake.  Ditch all remaining payload attachment  hardware.  Then continue do another breaking burn to do reentry experiment with 2nd stage?  Could be. 

Between zone 1 and zone 2 is the south Pole.  Is my assumption correct they are not allowed to dispose hardware there for environmental reasons or no limitations?
« Last Edit: 05/18/2018 12:11 PM by Heinrich »

Offline ZachS09

Just read over the newly-released press kit; how is the second stage going to reach a circular orbit of 625 kilometers, using one restart, from the initial orbit of 490 kilometers?

I thought three burns would be necessary.
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Online vaporcobra

  • Full Member
  • ****
  • Posts: 981
  • Tacoma, WA
  • Liked: 1616
  • Likes Given: 2108
Just read over the newly-released press kit; how is the second stage going to reach a circular orbit of 625 kilometers, using one restart, from the initial orbit of 490 kilometers?

I thought three burns would be necessary.

It's possible to change periapsis and apoapsis at the same time. The rough analogy is a right triangle, where you can achieve the same two-step X and Y axis movement by taking the hypotenuse. Just more complicated :D