Both of these photos are thought provoking (well for me anyway).
If the rocket was travelling entirely within its exhaust plume it would be a lot hotter, the air a lot turbulent so it must fly in slightly sideways for best control and drag when the air speed is high.
It's quite a balancing act... only at the end does it stand and go vertical.
My impression is that the angle of attack used within atmosphere generates useful lift. I've not heard of it as a thermal management technique. Especially in the early moments after atmospheric interface the aerodynamic heating is pretty ferocious (hence the intention to move to titanium grid fins) and I suspect that in that portion, which is probably the most challenging, the non-neutral angle of attack creates more thermal challenges than it solves.
But I don't have a good source reference to offer, and am open to learning better.
I presume by "flying sideways" you mean the long axis of the rocket is not coincident with the momentary centre of mass velocity ? :-)))
Turbulence is so unpredictable and thus the first order corrections are going to be with vanes and thrust vectoring. Countering turbulence perfectly would require feed-forward and anticipation of wind shear along the descent path. But maybe shedding vortices to one side by deliberate skew could be useful. The Shuttle used to do that alot, but in order to wash off massive kinetic energy by heating its tiles ie. it was intended that momentum be transferred from the Shuttle to the atmosphere by that technique. I once did a calculation on that. Over the course of about 20 minutes - typically high above the Pacific Ocean - the 'surfing' manoeuvres would require each square metre on the underside to dissipate at a minimum of 1 MWatt !! Alas that was it's ultimate downfall. In any case SpaceX has indicated that thermal damage ( peak heating to be exact ) goes like the speed to the 3rd or 4th ( ? ) power.
Cheers, Mike.
( edit ) I was watching an old 'Modern Marvels' episode last night about the US rail network. I found the Bailey Yard at North Platte fascinating in its 'gravitational sorting' of the cars. Anyway the most interesting thing was the regenerative braking by the locomotives on the downhill runs over the Sierra Nevada. The electric generators under reversal of current direction dump to a resistive load & thus create heat, in order to reduce the chance of a runaway train. Indeed it was quoted that without such a technique the massive trains loads could not be safely managed. Imagine if one could charge batteries on the Falcon first stage by running a propeller at the top end to drive a generator. Just sayin ..... :-)
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
And here I was thinking it just might be a bit of fuzzy logic. Intentionally not trying to align the rocket barrel, thrust vector and flight vector, but letting them wander inside limits.
P.S. I'd still like to know what kind of plane is seen taxiing in the first shot of the show.
There was another episode where the Enterprise went back in time and was caught in Earth's lower atmosphere. The Air Force sent up an F-104 starfighter to intercept the Enterprise. They ended up beaming the pilot aboard
(who was quite surprised : ) another great episode.
Bill
And while seated in the plane he materialized standing in the transporter, and vice versa when they beamed him back.
That is the episode I was talking about. Quite a bit of illogic in that one, and Spock saying "Logically, [blah blah blah]" doesn't make it logical. Good story and characters, though, despite the technical illogic. "Computed, dear." "Computer, you will not address me in that manner." "Computed, dear." "Maintenance note: my recording computer has a serious defect. Recommend it either be repaired... or scrapped. Compute." [hurt tone] "Computed."
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
( edit ) I was watching an old 'Modern Marvels' episode last night about the US rail network. I found the Bailey Yard at North Platte fascinating in its 'gravitational sorting' of the cars. Anyway the most interesting thing was the regenerative braking by the locomotives on the downhill runs over the Sierra Nevada. The electric generators under reversal of current direction dump to a resistive load & thus create heat, in order to reduce the chance of a runaway train. Indeed it was quoted that without such a technique the massive trains loads could not be safely managed. Imagine if one could charge batteries on the Falcon first stage by running a propeller at the top end to drive a generator. Just sayin ..... :-)
Hump yards are almost as old as railroads in the US and Canada, but their number has dwindled a bit as the nature of railroading has changed. Some humps have been removed and converted to intermodal facilities where containers and trailers are lifted on and off of flat or well cars. Technology has also improved the efficiency of the remaining hump yards, reducing the number of them that are needed.
Dynamic braking, of course, could not come into existence until the advent of the diesel-electric locomotive, although it probably existed earlier on electric railroads (power from overhead wire or 3rd rail). For the first 40-50 years of diesels, dynamics were an added-cost option, often skipped by flatland (or cheap) railroads. I believe that on electrified lines, sending the regenerated power back into the feed instead of waste heat is a relatively new development (30-40 years, maybe), probably enabled by better control equipment both on the trains and in the power distribution systems. (Previously, the concern was that one train suddenly sending power back into the wire could cause a power surge and dangerous burst of speed in another nearby train. It was probably also a problem with pre-solid state generating and rectifying equipment.) I know that Chicago Transit Authority's* newest cars, just bought a few years ago, are their first to have it.
*Celebrating today the 125th anniversary of the first L line, the Chicago and South Side Elevated, a.k.a. the Alley L because it was built over the alley behind the buildings instead of the street in front to exploit a loophole in the franchise ordinance and reduce right of way acquisition costs. It began operating with wood coaches and small steam locomotives on June 6, 1892. Much of the line is still in use as part of today's Green Line.
Okay, back to rockets.
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
Ok, if we must... but it is quite cool that railroad technology energy recovery has been around a long time but only recently made its way into F1 cars, next planes, then Mikes's prop rocket.
Returning to the flying sideways (aka a non zero angle of attack) -
During the re-entry burns, the surrounding air must be very turbulent, and you can see a wave / flame front ahead of the supersonic direction of travel. This must have a benefit of shielding the aft section as well during re-entry which is probably most vulnerable.
It's also probably easier to fly (generating lift) if part of the fuselage is in clean air and the other side in turbulent air.
edit: to arrive with zero kenetic energy, zero anglar momentum, and zero propellants...
edit: to arrive with zero kenetic energy, zero anglar momentum, and zero propellants...
Almost zero propellant. You still need a bit to gimbal the rocket engines to a lock position and retract anything else. Of course you also need your final safety margin.
Here is a dumb question, if it is all going to crap, is is cheaper to dump the stage in the drink or put a hole through the recovery ship?
Here's a long view a few seconds into the initial re-entry burn :
where clearly the booster is within a 'shroud' of the exhaust plume. There might be a mild angle of attack. The full sequence shows alot of billowing of the plume. There is an evident shock front where the exhaust gases reverse direction relative to the booster. It's hard to see from this view but the onboard footage indicates the grid fins being fully deployed at this point.
FWIW : Sorry, I'd missed mentioning what I thought was the most interesting analogy b/w rail car sorting and booster return. The desired braking is proportional to mass and requires a realtime assessment. The disconnected car cresting the hump is weighed and then variably braked prior to switching with the intent of it just rolling to a near stop with some existing manifest. This has feed-back and feed-forward components. Here the gravitational potential energy gifted by the height of the hump is paid out to various 'abrasive' modes. The clamping of the wheels in the braking section is rather like the re-entry burn. Along these lines of thinking then, the Falcon Heavy three-way return is going to be a real hoot ..... or a real **** up :-)
Also : you'd dump the stage as it's doomed either way. Keep the barge intact.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Where did my flying chimney
)
Where did my flying chimney go ? Oh, here it is :
I'd say that was a single/centre engine burn, with the usual hydraulics dribble to the left side of that.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Both of these photos are
)
Both of these photos are thought provoking (well for me anyway).
If the rocket was travelling entirely within its exhaust plume it would be a lot hotter, the air a lot turbulent so it must fly in slightly sideways for best control and drag when the air speed is high.
It's quite a balancing act... only at the end does it stand and go vertical.
AgentB, My impression is
)
AgentB,
My impression is that the angle of attack used within atmosphere generates useful lift. I've not heard of it as a thermal management technique. Especially in the early moments after atmospheric interface the aerodynamic heating is pretty ferocious (hence the intention to move to titanium grid fins) and I suspect that in that portion, which is probably the most challenging, the non-neutral angle of attack creates more thermal challenges than it solves.
But I don't have a good source reference to offer, and am open to learning better.
I presume by "flying
)
I presume by "flying sideways" you mean the long axis of the rocket is not coincident with the momentary centre of mass velocity ? :-)))
Turbulence is so unpredictable and thus the first order corrections are going to be with vanes and thrust vectoring. Countering turbulence perfectly would require feed-forward and anticipation of wind shear along the descent path. But maybe shedding vortices to one side by deliberate skew could be useful. The Shuttle used to do that alot, but in order to wash off massive kinetic energy by heating its tiles ie. it was intended that momentum be transferred from the Shuttle to the atmosphere by that technique. I once did a calculation on that. Over the course of about 20 minutes - typically high above the Pacific Ocean - the 'surfing' manoeuvres would require each square metre on the underside to dissipate at a minimum of 1 MWatt !! Alas that was it's ultimate downfall. In any case SpaceX has indicated that thermal damage ( peak heating to be exact ) goes like the speed to the 3rd or 4th ( ? ) power.
Cheers, Mike.
( edit ) I was watching an old 'Modern Marvels' episode last night about the US rail network. I found the Bailey Yard at North Platte fascinating in its 'gravitational sorting' of the cars. Anyway the most interesting thing was the regenerative braking by the locomotives on the downhill runs over the Sierra Nevada. The electric generators under reversal of current direction dump to a resistive load & thus create heat, in order to reduce the chance of a runaway train. Indeed it was quoted that without such a technique the massive trains loads could not be safely managed. Imagine if one could charge batteries on the Falcon first stage by running a propeller at the top end to drive a generator. Just sayin ..... :-)
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
And here I was thinking it
)
And here I was thinking it just might be a bit of fuzzy logic. Intentionally not trying to align the rocket barrel, thrust vector and flight vector, but letting them wander inside limits.
Gary Charpentier
)
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
Mike Hewson wrote:( edit ) I
)
Hump yards are almost as old as railroads in the US and Canada, but their number has dwindled a bit as the nature of railroading has changed. Some humps have been removed and converted to intermodal facilities where containers and trailers are lifted on and off of flat or well cars. Technology has also improved the efficiency of the remaining hump yards, reducing the number of them that are needed.
Dynamic braking, of course, could not come into existence until the advent of the diesel-electric locomotive, although it probably existed earlier on electric railroads (power from overhead wire or 3rd rail). For the first 40-50 years of diesels, dynamics were an added-cost option, often skipped by flatland (or cheap) railroads. I believe that on electrified lines, sending the regenerated power back into the feed instead of waste heat is a relatively new development (30-40 years, maybe), probably enabled by better control equipment both on the trains and in the power distribution systems. (Previously, the concern was that one train suddenly sending power back into the wire could cause a power surge and dangerous burst of speed in another nearby train. It was probably also a problem with pre-solid state generating and rectifying equipment.) I know that Chicago Transit Authority's* newest cars, just bought a few years ago, are their first to have it.
*Celebrating today the 125th anniversary of the first L line, the Chicago and South Side Elevated, a.k.a. the Alley L because it was built over the alley behind the buildings instead of the street in front to exploit a loophole in the franchise ordinance and reduce right of way acquisition costs. It began operating with wood coaches and small steam locomotives on June 6, 1892. Much of the line is still in use as part of today's Green Line.
Okay, back to rockets.
David
Miserable old git
Patiently waiting for the asteroid with my name on it.
David S wrote:Okay, back to
)
Ok, if we must... but it is quite cool that railroad technology energy recovery has been around a long time but only recently made its way into F1 cars, next planes, then Mikes's prop rocket.
Returning to the flying sideways (aka a non zero angle of attack) -
During the re-entry burns, the surrounding air must be very turbulent, and you can see a wave / flame front ahead of the supersonic direction of travel. This must have a benefit of shielding the aft section as well during re-entry which is probably most vulnerable.
It's also probably easier to fly (generating lift) if part of the fuselage is in clean air and the other side in turbulent air.
edit: to arrive with zero kenetic energy, zero anglar momentum, and zero propellants...
AgentB wrote:edit: to arrive
)
Almost zero propellant. You still need a bit to gimbal the rocket engines to a lock position and retract anything else. Of course you also need your final safety margin.
Here is a dumb question, if it is all going to crap, is is cheaper to dump the stage in the drink or put a hole through the recovery ship?
FWIW : Sorry, I'd missed
)
Here's a long view a few seconds into the initial re-entry burn :
where clearly the booster is within a 'shroud' of the exhaust plume. There might be a mild angle of attack. The full sequence shows alot of billowing of the plume. There is an evident shock front where the exhaust gases reverse direction relative to the booster. It's hard to see from this view but the onboard footage indicates the grid fins being fully deployed at this point.
FWIW : Sorry, I'd missed mentioning what I thought was the most interesting analogy b/w rail car sorting and booster return. The desired braking is proportional to mass and requires a realtime assessment. The disconnected car cresting the hump is weighed and then variably braked prior to switching with the intent of it just rolling to a near stop with some existing manifest. This has feed-back and feed-forward components. Here the gravitational potential energy gifted by the height of the hump is paid out to various 'abrasive' modes. The clamping of the wheels in the braking section is rather like the re-entry burn. Along these lines of thinking then, the Falcon Heavy three-way return is going to be a real hoot ..... or a real **** up :-)
Also : you'd dump the stage as it's doomed either way. Keep the barge intact.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal