h a l f b a k e r yExpensive, difficult, slightly dangerous, not particularly effective... I'm on a roll.
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I’ve seen it said (but will have to check and provide
links)
that the kinetic energy of a hypervelocity warhead
arriving
from orbit is so overwhelming that nuclear or chemical
explosives are unnecessary. I suspect that’s the reason
for
some moratoria on space weapons.
I don’t support
the development or escalation of military
technology or influence, particularly the militarisation of
space, but I do acknowledge that we have had some 70
years
of
“relative” global peace, in part because of nuclear
weapons.
So this is an idea about something that might be
technically possible, without an explicit view on whether
it’s a good thing or not.
As of January 2019, more than 128 million bits of debris
smaller than 1 cm (0.4 in), about 900,000 pieces of
debris
1–10 cm, and around 34,000 of pieces larger than 10 cm
were estimated to be in orbit around the Earth.
And it’s worth noting that Spacex Starlink has started it’s
programme to add 12,000 satellites to LEO.
These will be in a highly diverse set of orbits, and with a
great range of orbital vectors. A sufficiently advanced
space administration could send a vehicle to intercept
appropriate, massive debris objects (say dead satellites),
and compact them into a dense mass (perhaps with some
degree of structure/ablative shielding) to maximise post
re-entry integrity and kinetic energy.
Such a mission could easily be posed as “a service to
mankind” clearing space junk. But it could also have
very
significant strategic value.
Any such vehicle would need to have very good
manoeuvring, tracking and capture capability. But
nothing beyond current technology.
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OK, to begin with, are hyperkinetic weapons really
comparable to nuclear warheads? Consider 1000kg of
material travelling at 10km/s. Its kinetic energy is otoo
10^13
Joules. This is (surprisingly; at least I was surprised) not
manifold different from the energy of a 1000kg fission
bomb. So, you get an A for that one. |
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However, does this mean that 1000kg of orbiting mass is as
lethal as a nuclear warhead? Not really. To get it to hit the
surface of the Earth at 10km/s, you need to put a lot of
energy into it. In particular, you have to change its orbit
quite drastically - you'd want to put it in a very elliptical
orbit, and then tweak it so that the Earth got in the way. In
effect, you've got to put in most of the kinetic energy
before you can drop it on someone. |
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Another option would just be to decelerate it, so that its
(originally circular) orbit decays and it spirals down to the
ground. But that still means you've got to put the energy in
to slow it down; and most of that energy will be lost by
aerobraking during re-entry (even if your 1000kg of stuff
doesn't just burn up). |
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In effect, having a mass in a roughly circular Earth orbit is
energetically equivalent to having it sitting on the ground*.
If you want to slam it into a city at high speed, you've got to
put that speed into it first. |
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I've glossed over a few details, and it'll take a while to dry,
so please don't touch it in the meantime. |
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*This whole discussion ignores gravitational potential
energy, but the GPE of a 1000kg mass orbiting at say 300km
above the earth is only 3x10^8J, which is trivial compared
to kinetic energies. That's how much energy you could
deliver if you could just stop the orbiting mass in its tracks
so that it fell straight down; and even that energy would be
mostly lost as reentry heat. |
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Having paid an excruciating price (in energy) to haul the stuff out of your planet's gravity well, why not collect it up and do something constructive with it right where it is ? You have huge amounts of free heat (solar input) and there are probably a proportion of the photovoltaics that can be re-used. It will more than likely be something of a steampunk/Heath Robinson (Will Robinson? ) job, but you'll learn a lot in the process. |
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Of course there will probably be quite a few deaths along the way, but all progress comes with a price tag. |
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//A for that one// Thanks! <proudly showing off
badge/> |
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I was also surprised when I came across this. |
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There are other benefits to hyperkinetic missiles
from orbit: there’s no launch signature, very little
warning, and they’re essentially unstoppable. |
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Yes, disadvantages too. Orbital mechanics are
complicated, and require energy/delta-v/fuel. Re-
entry is essentially blind, and some energy is lost
to atmospheric heating. |
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I suspect loss to heat is competitively small- most
orbital reentries are designed to maximise this by
approaching at a shallow angle to bleed off ke
(aerobraking/aerocapture etc) - this would be the
opposite, presumably 100km straight through. |
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[8th] yes, it would be far better to harvest the
materials and components in orbit to make
something useful and beneficial to mankind.
Rather than killing people. Are you feeling ok? |
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At some point, someone will presumably build a space-pirate-
machine that simply wanders from satellite to satellite,
stealing a few solar panels from this one, an antenna from
that one... and using them to build an ever-more-powerful
space-pirate-machine. |
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Actually, given the amount of gold in spacecraft (thermal
shrouding; all those very expensive aerospace connectors), an
orbiting cannibalistic refinery might be the way to go. |
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//misfiled from orbit// Captain, it seems we were wrong
when we filed that one under S for Satellites... |
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That was quick! Already corrected |
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Bearing in mind [Max]'s first annotation, one way to
effectively use the kinetic energy stored in space junk
would be to use a long tether from a second satellite to
sling the junk at the target. You need two large
satellites. The first is orbiting east like most satellites,
picking up the space junk and compacting it. The second
is launched into an orbit in the opposite direction, but at
a slightly higher or lower orbit. To launch the collected
trash, wait until the two orbits happen to line up
somewhere above and not too far from the target.
Launch a tether that snags the junk as it goes past. The
junk starts spinning around the other satellite on the end
of the tether. Release the tether at the right time to hit
the target. I'm not sure if you want to try to make the
second satellite massive enough that it's orbit isn't
disturbed too much, or if you just make it about the same
mass as the projectile and send it sailing up as the other
is thrown down. |
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Remarkably elegant, [scad]. |
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// Are you feeling ok? // |
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Just lulling you into a false sense of security. |
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Presumably there must be such a thing as "Lulling someone into a false sense of insecurity" which sounds like it could be usefull in some circumstances. |
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