Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. ×

Pluto Probe Delayed 23

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."
This discussion has been archived. No new comments can be posted.

Pluto Probe Delayed

Comments Filter:
  • 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?
    • Re:Huh? (Score:4, Insightful)

      by Anonymous Coward on Wednesday January 18, 2006 @05:39AM (#14497924)
      And? Couldn't a few feet difference here mean thousands of miles later on, because of an altered trajectory?
    • 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.
    • by a5y ( 938871 )
      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.

    • 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
    • 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 a
  • by mstrcat ( 517519 ) * on Wednesday January 18, 2006 @07:42AM (#14498276)
    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.
    • 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 var

  • by Starker_Kull ( 896770 ) on Wednesday January 18, 2006 @07:59AM (#14498320)
    ...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...
    • 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.
    • by StupendousMan ( 69768 ) on Wednesday January 18, 2006 @11:28AM (#14499675) Homepage

      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.

    • 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 Plu
      • 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 l

    • 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,
    • 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.
  • Does this mean the probe for Uranus won't be ready in time, as well?
  • by PianoComp81 ( 589011 ) on Wednesday January 18, 2006 @11:26AM (#14499666)
    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/ [floridatoday.com])

Those who can, do; those who can't, simulate.

Working...