ULA’s Atlas 5 today successfully launched three U.S. military satellites


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Three U.S. military satellites, one to provide communications and the other two testing experimental engineering, were successfully launched today by ULA’s Atlas 5 rocket.

The leaders in the 2018 launch standings:

11 China
7 SpaceX
4 ULA
3 Japan
3 Russia
3 Europe
3 India

The U.S. is once again tied with China for the most launches this year.

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10 comments

  • Kirk

    With five strap-on SRBs, that Atlas leapt right off the pad! Here’s the video, with T-10 sec. at 20:47, SRB separation shortly after 22:40, and an interesting view of fairing separation showing significant flexing shortly after 24:30.

    I’ve seen that sort of flexing on separated Ariane 5 fairings in their webcasts, but I’ve not noticed it with Falcon 9 launches. I don’t know if that is just a function of camera placement and how soon the separated fairing becomes visible, of if it is due to the separation method and the ability of their fairing structure to dampen the oscillation.

    https://www.youtube.com/watch?v=YbOg_4rrJxc&t=1230

  • Dick Eagleson

    I believe the Atlas V and Delta IV fairings are shed via use of pyrotechnic charges (aka “explosive bolts”). Falcon 9 uses no pyros to do anything, including stage separation, fairing detachment and payload deployment. All are accomplished via helium gas pneumatic cylinders and/or springs. Pneumatic pushers and springs do not impart nearly as much excess energy to a fairing half as do pyro charges. That may explain the lack of extravagant flexing on the part of SpaceX’s payload fairing halves.

  • A question for the engineers: My first theory for the significant flexing was that, because ULA does not have any plans to recover the fairings, they build them lighter weight than SpaceX, which allows for more flex. I then thought that this theory made no sense, since all the fairings have to be made to resist the Max Q of launch.

    Could the reuseability plans of SpaceX still be a factor that could explain its lack of flexing?

  • Kirk

    Here is a few seconds of low frame rate video of a separating and flexing fairing half from January’s Ariane 5 launch (the partial failure one where they programmed the incorrect azimuth). It switches from animation to downlinked video at 3:45.

    https://www.youtube.com/watch?v=g47aftHgOnk&t=220

  • Kirk

    Here is the March 30 Iridium NEXT 5 Falcon 9 launch. Fairing separation is at 25:19, and it takes 5 seconds before a fairing half comes into view of the engine camera, but while it is farther away than the Atlas V or Ariane 5 fairings were when they were first visible, its silhouette is clear, and it doesn’t display the flexing.

    https://www.youtube.com/watch?v=mp0TW8vkCLg&t=1513

  • Edward

    When they say that size matters, believe them.

    Although SpaceX may have been concerned about damage that may occur due to the flexing and worked to reduce it, SpaceX’s fairings are somewhat smaller than the very large fairing on the Atlas V that we watched and smaller than the large fairing on Ariane’s January launch. The added length can give more opportunity for flexing and more mass to make for greater amplitude of the flexing, making it more visible than for the Falcon’s much smaller fairing.

    I also agree with Dick that the lower shock of the pneumatics provides for lower stresses (thus less strain, or flexing) on the various parts of the rocket, including the fairing.

  • pzatchok

    Max Q and the stress of separation are two vastly different dynamics.

    During Max Q all the stress is pushing in on the fairing. During separation a huge amount is placed on the inside of the fairing as it opens to the force of the passing atmosphere.

    Once it makes it to separation the other one use companies don’t care about flexing after Max Q.

    I bet Space X takes this into account in order to keep the flexing down and thus make the fairing reusable.

    As those fairings flex the fibers they are made off with break and the layers will separate thus making them not reusable. Stop the flexing and they are instantly reusable.

  • Kirk

    I agree with your thesis but take issue with “During separation a huge amount is placed on the inside of the fairing as it opens to the force of the passing atmosphere.”

    Isn’t aerodynamic pressure at the time of fairing separation almost entirely insignificant, even for an object as large and “fluffy” as a fairing half? While the fairing protects the payload from both dynamic pressure and aerodynamic heating, by the time of separation aren’t velocities and pressures such that the latter term dominates? Separation is usually timed for when aerodynamic thermal flux drops a bit below that of Total Solar Irradiance. From the Falcon User’s Guide: “4.3.8 Free Molecular Heating: The payload fairing will nominally be deployed when free molecular aero-thermal heating is less than 1,135 W/m^2. Other fairing deployment constraints can be accommodated as a standard service, although they may modestly reduce vehicle performance. Please contact SpaceX regarding mission-unique fairing deployment requirements.” I believe that by this point, actual dynamic pressure has dropped so low that foil on the payload isn’t even disturbed by the force of the passing atmosphere.

  • Edward

    Kirk wrote: “I believe that by this point, actual dynamic pressure has dropped so low that foil on the payload isn’t even disturbed by the force of the passing atmosphere.

    Correct. Thermal blankets (AKA multi-layer insulation) are located on many areas of the outside of many satellites and are made of thin mylar coated with appropriate materials to give the desired thermal properties. Some can be seen in the second stage engine compartment in the SpaceX launch videos, too. By the time of fairing separation, there is not enough force of the passing atmosphere to harm these blankets, antennas, reflectors, solar arrays, or any of the other delicate items unaerodynamically protruding from the payload.

    I think that pzatchok’s comment about the aerodynamic force at separation overestimates this force. I think that the major forces are those of the separation mechanisms; a lesser force is from the accelerating rocket on the bottom of the fairing, for the fraction of a second until the fairing comes off the upper stage; but the atmosphere provides an even smaller force though this force would be continuous, not transient. I think that the vibration we saw in the videos comes from the forces of the separation of the halves.

    Heating of the fairing is a problem, just as the SR-71 heats up during supersonic flight. The heat passes to the interior and can threaten portions of the payload. I worked on a satellite with a new design for “bumpers” between the solar array panels (launch vibrations could make the solar array panels flex and hit each other), and on launch the bumpers got a bit warmer than expected and stuck together, causing one of the panels to fail to deploy. (Years later, the panel finally deployed, as there was a continuous force on the sticky bumpers, due to the deployment springs.)

    Here is a link to answers to a question about winds and heating at fairing deployment. Notice that one of the answers links to several rockets’ customer user manuals.
    https://space.stackexchange.com/questions/20012/how-strong-and-hot-is-the-wind-on-the-payload-after-the-fairing-is-deployed-at

    Coincidentally, I had reread the SpaceX Payload User’s Guide a couple of weeks ago (engineers do the strangest things for amusement, but I was looking for vibration information, such as in section 4.3), page 36 gives an envelope for a payload to fit within.
    http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf

    ULA also provides some payload envelope information:
    https://www.ulalaunch.com/rockets/atlas-v

    Ariane5_Users-Manual_October2016.pdfPage 3-10 shows vents for removing the pressure within the fairing, and pages A5-2 and A5-3 give payload envelopes (usable volumes).

    What strikes me is that there does not seem to be any reduction in envelope near the base of the fairing to account for the flexing that we see on the jettisoned fairings. This tells me that the first inward flection of the fairing does not occur until after the fairing is clear of the payload.

    Because I already have multiple links (so Robert already has to moderate this comment), and since you, dear reader, are interested enough to have read this far, here is a link to answers to the question of why fairings are so expensive:
    https://space.stackexchange.com/questions/14780/what-makes-a-payload-fairing-so-expensive

  • Kirk

    Thank you, Edward, for the very informative post.

    Is it appropriate to ask you what mission had the sticky solar array panel bumpers?

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