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#326 2023-10-07 09:06:02
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
Void:
Regarding pressures exerted upon heat shields, and maybe foam construction, yes, there is pressure, and the peak of it occurs at the peak deceleration gee point during hypersonic entry. The heat shield material (and vehicle structure) have to be able to endure that pressure. Some materials can, others cannot, depending upon how much is applied, which varies dramatically with entry conditions and which planet.
If you know the mass and dimensions of the entering object, and you know the expected peak deceleration gees, then (peak gees) x (standard acceleration for 1 gee)x (mass of object = the decelerating force. The usual reference area is the frontal blockage area, which for most is the area of a circle at the heat shield diameter. The (decelerating force) divided by (reference area) = average pressure exerted upon the heat shield, which is not a uniform pressure distribution. The max pressure is located at the stagnation point (usually at or near center of the heat shield, but offset some if angled to generate lift forces), and it is roughly twice the average pressure.
The steeper your entry path angle below local horizontal, the higher your peak gees, and on Mars the more likely you are to smack the surface before you even get to slow down very much. Peak gees occurs very near the end of the aerobraking trajectory, because not until then has the air density become as significant as it is going to get.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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#327 2023-10-07 12:27:59
- Void
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- Registered: 2011-12-29
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
GW Johnson,
Thank you for your tolerance, and the assistance to learn. Knowing the limits helps for understanding what is real and what could possible be made real.
I do now tend towards a more modest notion of hard landing materials, probably by ejecting them from a spacecraft at low altitude, but I understand that even that has quite a lot of limitations.
If I continue with the notions somewhere in terraforming, perhaps it will not alloy you too much.
I am still interested in the possibility that captured pressurized air in a metal balloon might allow a thrust in the near impact mode to reduce speed. Currently I assign that a maybe.
The value of the products that might be landed by any method will be limited, and probably useful only for a small period of time of time during the setup of a base, I feel, as eventually a Mars or Moon base needs to create the bulk of its resources itself from materials at hand.
Done
End 
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#328 2023-10-07 12:36:08
- kbd512
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- Registered: 2015-01-02
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
GW,
Vought and Lockheed HVMs were cancelled because they had very short maximum ranges (3km to 5km) compared to AGM-65 (22km+) and AGM-114 (8km to 11km). Despite their much lower cost, relative to existing longer-ranged anti-armor missiles like Maverick and Hellfire, they had to be launched from distances very close to the maximum firing ranges for automatic cannons like the GAU-8 (1.2km to 3.7km). A 35mm (Oerlikon KDA at 4km) or 40mm (Bofors L70 at 4km) automatic cannon have very similar effective engagement distances when firing APFSDS rounds. Our much less powerful 20mm Phalanx Close-In Weapon System fires Tungsten APFSDS darts at incoming missiles and aircraft, at ranges between 1.5km and 5.5km, for example. The US Army's variant of Phalanx can shoot down 120mm mortar shells, so it's exceptionally accurate. The combination of Ku-band radar and IR / UV dual-band FLIR makes detection and engagement a high-probability event. As software target discrimination improves, these systems can categorize, prioritize, and cooperatively engage what they're firing at.
More importantly, 5km was well within the effective range of all then-existing MANPADS, such as the American FIM-92 Stinger and Soviet 9K35 Strela and vehicle-mounted 9M37 (a more powerful version of the 9K35, same seeker / electronics with a larger warhead and longer flight range). While an enemy armor column was losing vehicles to our HVMs, much more expensive tactical fighters like our A-10s and F-16s would be lost to Soviet MANPADS and radar-guided AAA like the ZSU-23-4 Shilka or radar-guided variants of the older but longer-ranged ZSU-57-2.
I think most pilots discount how lethal the modern versions of these short range radar / EO / IR-guided automatic cannon and small missile systems can be. They're the reason why you never want to intentionally allow your jet to wander inside their maximum firing range. Your fighter weapons, kinetic or warhead based, will be quite effective against armor, but their equally lethal weapons will transform your jet into confetti when they find their mark. I think it's a good thing we never had to fight the Soviets in a Fulda Gap scenario. Losses would greatly resemble WWII casualty levels. The majority of A-10 and F-16 kills were achieved in Iraq by firing the AGM-65 missile outside the effective engagement ranges of these short range defense systems, not the GAU-8. Short-range high velocity cannon systems were a weapon of last resort, not the primary go-to.
The array of short / medium / long range modern IADS deployed in Ukraine has demonstrated that air supremacy requires destruction of enemy air defenses first. If either or both sides fail to do this first, flying at any altitude above the battlefield is a very risky proposition. S-300 / S-400 / Patriot, Buk / AIM-120, AIM-9 / IRIS-T are all starting to live up to their hype. If there are no technical issues with the employment (radar down / unavailable) and the operator is paying attention, the odds are stacked very firmly against your first-encounter / only-encounter survival rate. If you survive that gauntlet of missile systems, giving your enemy one last shot at destroying your combat jet with Stinger / Strela / StarStreak (British origin HVM MANPADS), is not a good way to lead a long and healthy life as an attack jet pilot.
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#329 2023-10-08 13:37:11
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
The effects I was describing was for an updated bazooka tube weapon to use against tanks and bunkers, by infantrymen on the ground. Two guys under my supervision developed the rocket motor for that application, which was a graphite fiber-epoxy wound case 3.8 inch diameter, pressure-tested to 4000 psig.
We fired it several times with a reduced-smoke composite propellant, that was very nearly smokeless, but not quite. With a min smoke double base, it was essentially smokeless, but at reduced impulse delivery. Either way, it could blow the ever-loving "s**t" out of whatever it was aimed at, without any explosive warhead at all. The original bazooka round used the original shaped-charge warhead design.
The thing many did not understand, is that with a 1 or 2 second flight time to a target up to a mile away, active guidance was impractical, so smoke didn't matter for that issue. And reduced smoke is good enough to hide the infantryman who fired it. The thing should have been an unguided line-of-sight weapon, like the original bazooka, just 5 times faster flying. It would have also made the Russian RPG bazooka-like weapon obsolete.
Like I said above, the prime screwed this up trying to put active guidance on it. That's why the Army never bought it. We did that work more than 30 years ago.
GW
Last edited by GW Johnson (2023-10-08 13:40:11)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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#330 2023-10-09 19:49:58
- SpaceNut
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- From: New Hampshire
- Registered: 2004-07-22
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
Typically, something like this one
The one we were working with had a clamp on ratchet handle that set the down range distance inclination, which required it to be twisted to raise that elevation of launch.
What I worked on was an electronic version of this that gave a led readout and a cant indication as to whether it was set to go to the right or left of the center line.
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#331 2023-10-10 10:03:21
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
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Re: Ballistic Delivery of Supplies to Mars: Lithobraking
One of the advantages of a hypervelocity round over slower conventional rounds is that you no longer need a sophisticated sight that allows for trajectory shape. With hypervelocity, the trajectory is a straight line, and all you need is a simple sight parallel to the tube bore.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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