h a l f b a k e r yTip your server.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
Football star Rob Gronkowski set a world record for
catching a football dropped 600 feet from a helicopter.
At some point, the terminal velocity of a football is the
same no matter
what height you drop it from, but I think if properly
designed, it could withstand the temperatures of re-
entry
from orbit, 17,000 MPH and get down to the same speed
the Gronk caught that ball at.
So the contest would be set out in the desert,
contestants
would spread out over a hundred square miles or so
ready
to try their luck and skill. An astronaut would be seen on
live video in his spacesuit outside the spacecraft ready
to
throw the ball when in position.
The throw would have to be incredibly precise so there
would be a hoop put about 100 yards in front of the
astronaut/quarterback that he would have to hit
precisely.
After a few minutes, the ball re-enters the atmosphere
turning white hot in the process, slows down and
eventually cools off and slows down to a catchable
speed.
I think.
Take this to an insane extreme.
https://www.cnn.com...ld-record-spt-intl/
I'd try my hand at this if I was wearing proper body armor, helmet etc. I'd certainly watch in on TV. [doctorremulac3, Apr 26 2021]
Slightly relevant?
Pizza_20Satellite
[pocmloc, Apr 26 2021]
Wood ablative heat shield
https://en.wikipedi.../Fanhui_Shi_Weixing
[bs0u0155, Apr 27 2021]
Super lightweight stuff
https://inhabitat.c...dense%20than%20air.
How does this behave during re-entry? [doctorremulac3, Apr 28 2021]
Chalkboard spaghetti.
https://penntoday.u...-math-meets-physics
[doctorremulac3, Apr 28 2021]
You think your spaghetti is impressive?
http://www.mhs.ox.a...mbnails=on&irn=9738
[pocmloc, Apr 28 2021]
Steak Drop
https://what-if.xkcd.com/28/
Mr Munroe doing it his way... [neutrinos_shadow, Apr 28 2021]
Starlite
https://en.wikipedia.org/wiki/Starlite
[bs0u0155, Apr 29 2021]
[link]
|
| |
All that money they spend on the hi-tech ceramic tiles to protect spacecraft from burning up on re-entry. They could just use deflated footballs to coat the leading edge of the shuttle and other returning craft. |
|
| |
I think this would be an interesting design challenge. |
|
| |
How do you get something to survive a couple of
thousand degrees and incredible pressure then be
light enough to get down to a slow terminal velocity
while being cool enough and slow enough to catch? |
|
| |
That's the interesting challenge right there. |
|
| |
Magnus Forces might make this particularly tricky if
the ball goes into any kind of spin on the way down. |
|
| |
The trajectory issue would be difficult even if a
machine did it, but to have the astronaut throw it,
even tricker. A few inches in one direction or
another is a few hundred miles by the time it got
to the impact point. |
|
| |
There's other stuff you could do with this as well.
Just dropping stuff that anybody could catch.
Goodwill sort of stuff like, I don't know, what could
you catch falling from the sky that would make you
happy? |
|
| |
God, the only thing that came to my mind is
money. Silicon Valley really has warped my soul. |
|
| |
By the way, scratch the term "impact point",
something like "Happy funtime catch zone." might
be better. |
|
| |
There's been some discussion of re-entry heating on here before, related to pizzas I think, but I'm struggling to find much |
|
| |
I'd rather they tossed Gronk out and we could go looking for
him, (and his parachute of course.) hahahaha. |
|
| |
A snowball, in August
A letter from my son
Hot stew when I'm hungry
A crispy buttered bun
The sky has its limits
No largess by the ton
But surely some trifle
My favorite team's home run?
|
|
| |
The things that we wish for
could fill a Scrooge's home
But listen, dear reader
Allow your thoughts to roam
to things that we're blessed with
before our pains bemoan
The sky grants us blessings
it gave us all we own.
|
|
| |
When rain falls remember
the fruit out in the field
how richly the harvest
that rain and sun will yield.
The brightness, the comfort
the smiles that are revealed
It's not just the sunshine
but from the bad, a shield.
|
|
| |
From there in the vastness
the comet and asteroid
the gamma, the beta
the power of the void
against the flares and nova
our world a guard employed
The air and the magnet
leaving us undestroyed
|
|
| |
When life gives you lemons
at least you have the tree
Snow storms bring their danger
but watch your children's glee!
An angel or a snowfort
A mountain you can ski.
Dark clouds have their lining
So gratitude is key. |
|
| |
Wow V, that's beautiful. You wrote that? |
|
| |
//All that money they spend on the hi-tech ceramic tiles to
protect spacecraft from burning up on re-entry// //I think
this would be an interesting design challenge// |
|
| |
It's the friction of the atmosphere against the object
achieving re-entry of course, which leads me to wonder,
surely if you could match that orbit to the speed of the
atmosphere's rotation while lowering the object through it
slowly enough you could avoid that friction entirely? |
|
| |
You mean drop it from geosynchronous orbit? |
|
| |
Yes, that's a great idea but don't you have to be
pretty far out to do that? I think you have to have
enough speed to stay in orbit so to achieve that
you have to be really far away. If you're
geosynchronous any closer you just fall with the
football you're trying to drop. You'd just be
traveling at whatever the Earth rotates at, 3,500
MPH or something? (I'm probably totally off) but
definitely not fast enough to stay in orbit which
has to be 15,000 MPH I think. |
|
| |
So you could drop it from way out there where we
put the satellites that stay over a set point on
Earth, but not much chance of predicting where it
lands. |
|
| |
You could slow it down by shooting it out of a
cannon or attaching rockets to it, but to slow it
down to a standstill over a spot on Earth means
accelerating it to 15,000 MPH relative to the
spacecraft going that fast in the other direction, so
only rockets
would do that. Not even a railgun can get much
beyond 5,000 MPH I'm reading. At some point it
gets pretty pointless. Good luck getting the
taxpayers to foot the bill for that. |
|
| |
So I think you're stuck with engineering a football
that can survive thousands of degrees then be light
enough, slow enough and cool enough to catch
when it reaches terminal velocity. |
|
| |
Let me know when you come up with the design.
I'll be in my office. |
|
| |
By the way, correct me if I'm wrong, but didn't
Arthur C Clark, the 2001 author invent
geosynchronous orbit? I think he did. |
|
| |
I don't know one way or the other [any atmospheric &
orbital
mechanics experts out there?] but I can't help suspecting
that geosynchronous with the atmosphere 'might' not be
(entirely)
geosynchronous with the planets surface? if you have a
smooth ball floating & spinning in a bowl (made of
frictionless material for the purpose of this thought
experiment) of water does the
water spin at the same speed as the ball or is some of the
energy lost to heat dissipation in the friction transferring
the
motion to the water & it spins a bit slower than the ball? |
|
| |
//How do you get something to survive a couple of thousand
degrees and incredible pressure then be light enough to get
down to a slow terminal velocity while being cool enough
and slow enough to catch?// |
|
| |
The key is to go for an ablative heat shield like the Chinese
oak version <link>. Then, you can throw a re-entry capable
spacecraft but catch a football, if you get your calculations
exactly right. Otherwise Gronk might have to catch a 50lb
lump of scorched wood. |
|
| |
I thought about that, and you're right. 1% off in your
calculation and the Gronk's got a pretty sizable hole
clear through his chest. |
|
| |
Guess you could do some kind of staging thing like
they do with other delicate stuff being de-orbited.
Heat shield separates and drops the football after all
that nasty re-entry stuff. Sort of cheating though, I
think the challenge of having one object that fills all
the criteria is what's interesting. |
|
| |
// I thought about that, and you're right. 1% off in your
calculation and the Gronk's got a pretty sizable hole clear
through his chest.// |
|
| |
What you'd want is an ablative heat shield that continues to
ablate when the football is pretty slow in thick-ish
atmosphere. Something like dry ice might do it, frozen
alcohol? Water ice isn't a good candidate because big
hailstones make it down OK. |
|
| |
//is some of the energy lost to heat dissipation in the friction transferring the motion// |
|
| |
Remember, the atmosphere has had 4 billion years to spin up to the rotational velocity of the earth. |
|
| |
Hey V, just read that again, kind of speechless.
Please publish that someplace or something. That
needs to be shared. |
|
| |
Share it, copy it, rewrite it, publish it. Information wants to be free. |
|
| |
You could make the football from aerogel. Should withstand the heat, be light enough to maintain a slower terminal velocity... and I like aerogel. It's funky. |
|
| |
The question is, what is meant by orbital velocity. After all ANY height or vector above a point of gravity will be some kind of orbit. Is it "an orbit that clears the atmosphere in all phases"? That would give a minimum and maximum velocity, but the minimum would be much, much lower than he maximum. If that's your definition you'll do best to have a circular orbit at the minimum permitted height. If you do that, though, the orbit will not re-enter except by slowing to a suborbital velocity. And if you're defining it as a suborbital velocity, well, it's tautological. |
|
| |
Why am I thinking of a
turtle called tortoise right now, something about the style I
think. |
|
| |
Dumb question: how do the lightest substances (link)
behave
during re-entry? I assume you need some mass to actually
drop into the atmosphere instead of just bouncing off
right? |
|
| |
Is this a correct assumption? So you're going to need to
generate some push against that atmosphere to get the
friction going. |
|
| |
I assume something like a feather would burn up during
re-
entry eh? What about this super light stuff? |
|
| |
[Voice], I love your poem. I would like to put it on my home
page. May I? I may also share it elsewhere where we speak of
gratitude's importance daily. This is incredible. |
|
| |
Hmm, sounds like a job for somebody fluent in spaghetti,
which is my name for what superbrainiacs put on a
chalkboard or whiteboard when they're designing something
I can't begin to comprehend. (link) |
|
| |
//I would like to put it on my home page. May I? // |
|
| |
Of course. Information wants to be free. I'm happy you guys like it. It seemed average to me. |
|
| |
I put the last line on my homepage, but to make up for
being so reverent (very bad form) I took the liberty of
matching up the rhythm in the lines a little bit. (I know,
even worse form!) |
|
| |
When life's giving you lemons,
at least you have the tree.
Snow storms may bring their danger,
but watch your children's glee!
An angel or a snowfort,
a mountain you can ski.
Dark clouds all have their lining,
so gratitude is key.
|
|
| |
xkcd did a What If about dropping steak (linky), which
covers some of the questions here. |
|
| |
That kind of makes sense to me, so I'm thinking 2fry's
aerogel football would do it. |
|
| |
I'm going to contact some scientists to find out. |
|
| |
Anybody want to place bets? Or want to submit
another design to go up against 2fry's? We have the
ablative shield but that would be too unpredictable I
think. |
|
| |
I'm going standard football covered with Starlite <link>. |
|
| |
So cornstarch, baking soda and glue. OK, sounds like I'm
being sarcastic but I've seen a video of the guy
demonstrating the stuff and if it's a farce it's a damn good
one. Looks pretty amazing. Hate that it's not being used
for anything. Sounds like he was overly protective of his
invention maybe. |
|
| |
Aerogel vs Starlight but a thin enough layer that you're
not adding much mass. |
|
| |
I'll add my design suggestion now. The ball is football
shaped only at sea level. In the vacuum of space it
expands to say... the size of a Volkswagon. This very large
but low mass for its size object would aerobrake with a
great deal of area high up but shrink as the atmospsheric
pressure increased. By the time it's at sea leval it's just a
catchable football. |
|
| |
If that wasn't enough to slow it down, you could have bits
of heat shield glued all over it that would pop off as it
shrunk but guess that's just another heat shield so yea,
just the expansion thing then. |
|
| |
I'll contact some sciency types at Stanford, MIT and
Oxford etc. I've done it once before regarding a subject
discussed here and was surprised at how eager these guys
were to assist if it's an interesting enough question. |
|
| |
Satellites in low Earth orbit go round in around 90
minutes whilst we are fixed on the Earth and go round in
24 hours. So we can definitely say low Earth orbit
satellites are going about 16 times faster than we are,
relatively speaking. |
|
| |
The radius of the Earth is about 6400000 metres so with a
bit of 2.Pi.R action we can calculate satellites move at
around 7500 metres per second. On the Earth we are
moving round at around 470 metres per second. |
|
| |
So all we have to do is slow down the football by around
7000 metres per second; around 25000 miles an hour.
That's a lot of speed to lose and I'm sure it can be solved.
Satellites in geostationary orbit go round in 24 hours but
given their distance above the Earth, something like
36000000 metres, they are travelling at around 3000
metres per second. A bit less speed to lose but the wait as
those footballs make the 36000 kilometre journey might
make it a dull spectator sport and we do have to think
about how to monetize the business model. |
|
| |
I suggest an alternative. We should speed up the Earth's
rotation. |
|
| |
If we increase the spin of the Earth so a day is now a
cheeky 90 minutes, the problem reduces somewhat. No
more rapid delta-v changes now. Low Earth satellites with
hopeful throwers can aim with more confidence and there
should only be a few minutes between throw and impact.
Plenty of time for some revenue generating adverts as
well as a nice cup of tea. |
|
| |
There would be some second order problems to solve but
I think it's do-able. We would have to change the working
day to fit into 90 minutes. Frankly, it's about time we
changed this. There might be tricky climate impacts but
surely nothing too serious. People at the Equator would
feel centripetal forces that are likely to counteract
gravity completely so there would be a whole new market
for weight loss holidays in the Tropics. The oceans might
escape into space and the planet might spin apart but
these feel like low risks so I'm not worried. |
|
| |
I think a football that could be blown up to the project echo
size thing is possible. That's an interesting engineering
challenge right there. |
|
| |
//the wait as those footballs make the 36000 kilometre
journey might make it a dull spectator sport and we do have
to think about how to monetize the business model.// |
|
| |
Good looking cheerleaders. Problem solved. |
|
| |
[DenholmRicshaw]; rotating the Earth at 1 rev in 90 minutes
is dangerously close to falling-apart speed: my calculations
(correct me if I'm wrong) put the "centripetal acceleration =
gravity" speed at 1 rev in 84.42 minutes (1h 24m 26.3s). |
|
| |
Yes, so we might need to strengthen the Earth a
bit but worth it for those weight loss holidays. |
|
| |
Same result but easier is to slow down the clocks. |
|
| |
//my calculations (correct me if I'm wrong) put the "centripetal acceleration = gravity" speed at 1 rev in 84.42 minutes // |
|
| |
That's no coincidence: after all, it's orbital velocity. |
|
| |
//Earth so a day is now a cheeky 90 minutes// |
|
| |
I expect that would have a fairly dramatic effect on the
Coriolis force and therefore hurricanes. Florida is in real
trouble. |
|
| |
It seems to me shorter days (in a fantasy world where gravity isn't effected) would lead to calmer weather, as the cold and hot air meet each-other more frequently and therefore don't have as much time to build up volume and large temperature differences. |
|
| |
//beetles the size of cars// |
|
| |
Not unless you unleash the terrifying Genetic Engineers and give them lungs. |
|
| |
//Genetic Engineers// or... raise them in a total-O2 atmosphere, then attach some solar-powered case fans before releasing them. |
|
| |
//a 21 tone rocket booster// I would pay to listen to that |
|
| |