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Pluto Probe Delayed

Posted by ryuzaki0 on from the better-safe-than-sorry dept.

setirw writes "Due to high wind conditions at the launching site, the launch of the NASA's probe to Pluto has been delayed for 24 hours. "The wind limit at the pad is 33 knots [and] we have exceeded that limit several times today," said NASA spokesman Bruce Buckingham." From the article: "Glitches with an Atlas 5 vent valve, a ground tracking station in Antigua and NASA's Deep Space Network also led to launch delays, though the wind concerns were omnipresent throughout those issues."

23 comments

  1. Huh? by voice_of_all_reason · · Score: 1

    From what I remember of physics, x and y forces do not affect each other on their own. If you roll a ball off a stair or the grand canyon, it will travel in the same parabolic arc until reaching the ground.

    So why does a horizonal force of wind have any effect on the vertical force of the thrusters? Won't the probe just end up exiting the atmosphere a few feet to the left or right, if at all?

    1. Re:Huh? by Anonymous Coward · · Score: 4, Insightful

      And? Couldn't a few feet difference here mean thousands of miles later on, because of an altered trajectory?

    2. Re:Huh? by Urkki · · Score: 1

      I'd imagine there's a real risk of the rocket actually breaking up because of the wind, or not just moving sideways but actually tilting ie changing direction. And the rocket is already close to it's limits, there aren't too big margins on structural strength or amount of fuel on rockets, as every extra gram on rocket structure is one gram away from payloal.

    3. Re:Huh? by a5y · · Score: 1
      If you roll a ball off a stair or the grand canyon, it will travel in the same parabolic arc until reaching the ground.

      If windsheer is enough to affect a plane landing on a runway, I feel it's safe to assume its a gamble to launch an expensive piece of kit under windy conditions.

      Either that of NASA should try making really big space kites.

    4. Re:Huh? by Vo0k · · Score: 1

      When it's up in the air, there's little risk, turbulences causing rotation as opposed to movement etc, no biggie. But if it's still on the ground, with the supports already removed, apply constant force over whole length, while only the base is supported, and it will tip over. Apply enough force to the upper part while not pushing the bottom part (winds 30m over the ground level are WAY stronger than just above the ground!) and it won't fly vertically up, it will just hit the ground. There's only so much of tilt the thrusters and steering fins can correct (expecially little at low speeds just after start). Anything above will make it crash.

      --
      Anagram("United States of America") == "Dine out, taste a Mac, fries"
    5. Re:Huh? by Starker_Kull · · Score: 1

      As you say, perpendicular forces do not affect each other. This mean the force of the rocket being lofted vertically will not affect the strong LATERAL force being exerted by the wind, including when the rocket is right by the launching gantry for the first few seconds. When the rocket is resting on the launch pad, the friction of the base on the pad exerts the requisite lateral forces necessary to keep it from sliding sideways - but the moment it lifts off, that goes away. Being pushed into the gantry at liftoff (when it has virtually no maneuver capabilities to prevent it) would be disastrous for obvious reasons. Yes, there is a certain amount of clearance between the two... just enough to tolerate winds up to the stated maximum.

      Disclaimer: IANARS

  2. wind limits on rocket lauches by mstrcat · · Score: 4, Informative

    Wind limits on rocket lauches are a combination of several things, just as most complex engineering problems.
            The structural forces placed on the structure from side winds are negligible when compared to the acceleration forces due to lauch.
            For the most part, it's not the final trajectory of the payload that sets them, as secondary burns and mid-course corrections are more than adequate to correct any small variation in the launch vector.
            More importantly is stablity of the rocket under side forces. Because of a rocket's tall slender build, the center of mass is far away from point of thrust (the engine nozzles). Any small horizontal motion of the center of mass with respect to the point of thrust can quickly lead to tumbling. It's this control problem that really determines the launch limits. A rocket is inherently unstable and requires dynamic control, typically small engines around the periphery of the main nozzle that can swivel to provide righting moment. As with any real control system there are limits to the perturbation it can handle, and this is translated into wind speed limits.

    1. Re:wind limits on rocket lauches by DerekLyons · · Score: 2
      Wind limits on rocket lauches are a combination of several things, just as most complex engineering problems.

      The structural forces placed on the structure from side winds are negligible when compared to the acceleration forces due to lauch.

      Negligible compared to acceleration forces is not the the same as trivial. (Especially since the wind forces manifest themselves in a direction other than that where the rocket is strongest - along the vertical axis.) Side loads can and do induce body bending and a variety of vibratory modes.
      For the most part, it's not the final trajectory of the payload that sets them, as secondary burns and mid-course corrections are more than adequate to correct any small variation in the launch vector.
      Assuming of course the variation is small, (defined as within the excess performance available). If the winds are strong enough, and the margin small enough, then they can in fact affect the final trajectory.

      All that aside, the winds that were the problem today were ground winds, not altitude winds. Right after launch the rockets ability to correct for errors is the least, leading to the possibility of impacting the tower. Another problem from ground winds is ensuring they are blowing in a direction that will carry any gases released (from the launch or from a failed launch) in the proper direction.

  3. For the rocket scientists out there.... by Starker_Kull · · Score: 3, Interesting

    ...If I read the mission description correctly, this probe is scheduled to be in the vicinity of Pluto and Charon only for a day - in other words, it is doing a fly-by. Why not try something more ambitious, like enter orbit around Pluto? I understand the heat/technical problems with actually landing on Pluto or Charon; but is the energy requirement to enter orbit rather than just flyby that large? I know the probe is getting a gravitational boost from Jupiter, so it shaves a few years off of the flight time, but if it didn't get that boost, wouldn't it arrive in Pluto's vicinity with less energy and thus be easier to put into orbit? Or is the extended time in space that much more likely to lead to failure? I don't have to explain the obvious payoff in terms of scientific benefits of a long-term orbit versus a one day fly-by...

    1. Re:For the rocket scientists out there.... by Tango42 · · Score: 2, Informative

      They want it to explore the Kuiper belt afterwards, so they would have to enter orbit and then leave it and build up the speed again, which would take a lot of fuel.

      It will be in the vicinity of Pluto for longer than a day - it won't be very close for that time, but it will be more than close enough for the work they want to do.

    2. Re:For the rocket scientists out there.... by StupendousMan · · Score: 3, Informative

      Quoth the parent:

      > is the energy requirement to enter orbit rather than just flyby that large?

      In brief, yes.

      (Warning: back-of-the-envelope calculations follow)

      In order to reach Pluto in a reasonable number of years, the probe must move very fast. Let's see ... very roughly, it goes 40 AU in nine years. That's about 4.5 AU per year, or a cruising speed of about 21,000 m/s.

      If you wanted to put it in orbit around Pluto, you'd have to decrease its speed to the orbital speed of Pluto, which would be a few hundred m/s. That means you'd have to decrease the speed by roughly 20,000 m/s ... or, to a good approximation, you'd have to remove all the velocity you had added to the probe in the first place. The mass of the probe is roughly 1,000 kg, so its momentum must be decreased from about (20,000 m/s) * (1,000 kg) = about 20 million kg*m/s to zero.

      To reduce the momentum, you fire an engine pointing backwards: the engine throws exhaust products forward at some speed, and the momentum they carry away reduces the remaining momentum of the probe. Chemical rockets have typical exhaust speeds of around 2,000 m/s, so to remove 20 million kg*m/s, you'd have to throw around 10,000 kg of mass out of your engine. (Yes, yes, it's more complicated than this, but for the purpose of illustration, it's close enough).

      But, wait a minute: the probe's mass is only 1,000 kg. It can't carry 10,000 kg of fuel and oxidizer, too. So it cannot slow itself down enough to enter orbit around Pluto. If you wanted to design a probe which could enter orbit, you'd have to make it carry huge amounts of fuel for this burn when it reaches Pluto ... but then you'd need an enormous rocket to accelerate the fuel and probe to 20,000 m/s in the first place.

      It just isn't practical. Sorry.

      --
      Michael Richmond "This is the heart that broke my finger."
      mwrsps@rit.edu http://stupendous.rit.edu
    3. Re:For the rocket scientists out there.... by Starker_Kull · · Score: 1

      Thanks for the back-of-the-envelope calculation... I suspected it was something like that. I presume the reason it is "easier" to orbit a probe around, say, Jupiter, is that a) It doesn't require quite the same velocity to get there in a reasonable amount of time, and b) Jupiter's stronger gravitational field means an orbit can be maintained at a higher velocity, so less speed needs to be burned off....

      Is there some fairly simple metric of "efficiency" of a rocket? I know with jet engines we like to get maximum mass flow per unit energy (since the most efficient way of transforming energy to momentum is maximum mass flow with minimum velocity change), but since the rocket carries it's own mass flow, so to speak, the options are far more limited... Any sources you can recommend for a curious amateur?

    4. Re:For the rocket scientists out there.... by BranMan · · Score: 1

      IANARS, but I don't think it takes one to see why they didn't try an orbit. I asked myself the same questions at first, then remembered how small Pluto is. Not much chance of slowing down to go into orbit - you need 25K mi/hr for escape velocity for Earth (IIRC) and the Jupiter slingshot will bump that to 37K+ to make the trip shorter. No way to bleed off that much speed - you'd need a Saturn V or more out there to do that. Or they could have bled the speed off at Jupiter and crawled out there to Pluto for decades. I know I wouldn't want to wait that long.
            I'd like to know why they didn't include an impactor though. Those are always fun, but probably not as useful as the instruments they'd have to leave behind.

    5. Re:For the rocket scientists out there.... by forkazoo · · Score: 1

      Aside from the other posts explaining the issues of needing ginormous rockets, we also don't know what we'd want to put on the orbiter/lander. Once we have a flyby, and we can get some detailed information about Pluto, we can go, "Well, this piece of data is really interesting - I want to know more about XYZ"

      If we make an orbiter without knowing some of the basics, we may send a big honking magnetometer and a camera (for example.) If Pluto has no magnetic field, and doesn't visually change much over time, then the orbiter doesn't get us any more real information than the flyby.

      Also, the flyby may be able to see some of the other stuff out there. We dont know what will be nearby yet, but we are currently scanning the heck out of that chunk of the sky. In ten years, we hope to know of several objects along the flight path that the probe can fly past after Pluto. This would be impossible with an orbiter.

    6. Re:For the rocket scientists out there.... by DerekLyons · · Score: 1
      I understand the heat/technical problems with actually landing on Pluto or Charon; but is the energy requirement to enter orbit rather than just flyby that large?
      Yes - because of the high speed that must be bled off. The only way to reduce that energy requirment is to accept a longer transit time - which increases the chance of failure.
    7. Re:For the rocket scientists out there.... by Danny+Rathjens · · Score: 1
      You can do that with nuclear propulsion which is what NASA wanted to do. Congress forced their hand, though.

      NASA Administrator Sean O'Keefe has said repeatedly that he favors putting off the mission until sometime next decade when nuclear propulsion systems could enable a probe to reach the distant planet faster and stay there longer.
      http://www.space.com/scienceastronomy/solarsystem/ pluto_options_020128-1.html

    8. Re:For the rocket scientists out there.... by KarMann · · Score: 1
      Not much chance of slowing down to go into orbit - you need 25K mi/hr for escape velocity for Earth (IIRC)....

      Actually, the "25K mi/hr for escape velocity" is irrelevant for these purposes; what makes it an escape velocity, after all, is that that's how much speed will be lost if it escapes from Earth. So something launched at exactly escape velocity will asymptotically approach 0 mi/hr; something launched at 26K mi/hr will approach 1K mi/hr (assuming the accuracy of 25K mi/hr).

      And of course, anything launched at less than 25K mi/hr will not escape Earth, and will stay in orbit around it (unless it gets too close to the Moon, or something like that).

      --
      ProofReading Markup Language - and yes, I find typos.
    9. Re:For the rocket scientists out there.... by shadowbearer · · Score: 1

      It's practical is you want to use an engine with a very high ISP, but it's not going to get there within the time alotted for the project budget :)

      SB

      --
      It's old. The more humans I meet, the more I like my cats. At least they are honest.
  4. And this is not on the Frontpage!? by Anonymous Coward · · Score: 0

    What's up?
    Need place for the upcoming 5 Apple stories?
    Slashdot - news for sheeple, stuff that's lame.

  5. Uranus? by smvp6459 · · Score: 1

    Does this mean the probe for Uranus won't be ready in time, as well?

    1. Re:Uranus? by Anonymous Coward · · Score: 0

      Pfft, that was launched a long time ago.

  6. Launch scrubbed for Wednesday as well by PianoComp81 · · Score: 3, Informative

    The launch has been scrubbed for Wednesday as well, because of a power outage in Maryland at the New Horizons control center

    (see http://www.floridatoday.com/floridatoday/blogs/plu tolaunch/)