For Questions That Don't Merit Their Own Thread

[55delta]

Re-reading The Martian, so I wonder. Could you send a probe with a food payload to land on Mars without a landing system and still have an ediably intact payload after landing?

[kerbiloid]

If the client prefers his food toasted and well perchlorated.
Also unlikely they 

Schiaparelli has crashed 

Quote

 with the parachute deploying at 12 km (7.5 mi) and 1,730 km/h (1,070 mph), and its heat shield releasing at 7.8 km (4.8 mi). However, the lander's inertial measurement unit, which measures rotation, became saturated (unable to take higher readings) for about one second. This saturation, coupled with data from the navigation computer, generated an altitude reading that was negative, or below ground level. This caused the premature release of the parachute and back shell. The braking thrusters then fired for about three seconds rather than the expected 30 seconds, followed by the activation of ground systems as if the vehicle had already landed. In reality, it was still at an altitude of 3.7 km (2.3 mi).^[59][60] The lander continued transmitting for 19 seconds after the thrusters cut off; the loss of signal occurred 50 seconds before it was supposed to land.^[61] Schiaparelli impacted the Martian surface at 540 km/h (340 mph), near terminal velocity.^[60]

Spoiler

 

An unguided container with food, with no heatshield, probably would break apart high in the sky, and definitely would miss a hundred kilometers.
So, Watney should make a cruise to find in the desrt its remains, lying around, with torn envelopes, covered with toxic dust.

I wonder why they author didn't put that food into a dismissed Titan 2 warhead.
It would survive and land more precisely.

Spoiler

 

On 5/17/2018 at 2:47 AM, cubinator said:

What do the Venera probes look like today? I can't imagine decades under that acid oven of an atmosphere would leave them in any sort of decent state.

Like a centimeter-thick titanium sphere about a meter in diameter, covered with dust.

Edited May 18, 2018 by kerbiloid

[Not Sure]

If something burns ALL of its mass when accelerating, (end burn mass is 0g) then does it technically have infinite dV? Is it technically traveling at light speed?

 

 

negative mass?

[kerbiloid]

Last molecule of the something can't throw anything back, so no more thrust.

Edited May 18, 2018 by kerbiloid

[Ultimate Steve]

I've seen this referenced in many places... Why can't a fluid flow through something (pipe, nozzle, etc) faster than the speed of sound?

[kerbiloid]

It can.
https://translate.google.com.tr/translate?sl=ru&tl=en&js=y&prev=_t&hl=ru&ie=UTF-8&u=http%3A%2F%2Fmash-xxl.info%2Finfo%2F578687%2F&edit-text=

[Not Sure]

2 hours ago, Ultimate Steve said:

I've seen this referenced in many places... Why can't a fluid flow through something (pipe, nozzle, etc) faster than the speed of sound?

Who said it can’t? That’s crazy! Ever hear of a Mach 2+ wind tunnel?

 

[55delta]

15 hours ago, 55delta said:

Re-reading The Martian, so I wonder. Could you send a probe with a food payload to land on Mars without a landing system and still have an ediably intact payload after landing?

I'll hedge this a little then and say that a heatshield would be for atmospheric entry instead of a 'landing system.' And yes, I know that a controlled crash is, in a purely technical system, 'a landing system.' I'll re-define the question then. How could a probe with payload deliberately crash on Mars and still have an intact payload? Additionally, would it be simpler to just use the landing balloons than a deliberate, controlled crash?

[Cunjo Carl]

3 hours ago, Ultimate Steve said:

I've seen this referenced in many places... Why can't a fluid flow through something (pipe, nozzle, etc) faster than the speed of sound?

I am completely unable to make good thoughts right now, but the effect is known as 'choked flow' and can be looked up under that name.

It's a really obnoxious effect, I'll tell you what.

I'll make a blind stab at remembering here, but no guarantees. I wish I could do you better, but hopefully this'll get you going in the right direction!

Spoiler

It's a viscous effect, not a kinetic/molecular one. The idea I've had in my head, and it's always worked for me in practice, but I'm not sure of it's veracity, so please take a shaker of salt.... Anyways, imagine the fluid is a bunch of tiny packets of volume. The speed of sound is how fast forces can travel between these packets for normal flow. If the packet of fluid right at the nozzle suddenly disappears (cause it flew away) the next packet in line has to wait for the speed of sound to notice it went missing, which controls the maximum volumetric flow rate out the nozzle, which in turn controls the max velocity of the same. It's been a long time since I had to derive the effect in fluid dynamics, but I believe it wound up being similar to the venturi effect in its energetic derivation... If I recall right, it's almost the same as deriving the speed of sound (which is for an isentropic =reversible process) except choked flow is a little more restrictive (it's for an adiabatic process). I think. You imagine a narrow tube with a high pressure fluid suddenly opening into a larger one, and find that while you get energy from increasing volume, you also lose energy to adiabitic expansion effects (little unavoidable mini shockwaves) or if the little tube had its energy in terms of flowing quickly instead, then you still gain energy from the increasing volume, but the energy turns into pressure (paradoxically) in the larger tube. Either way, you don't go above mach. Weird that.

 

[kerbiloid]

Though, unlikely a fluid can flow throw a pipe faster than the speed of sound of the pipe material, as probably the pipe would get mechanically unstable.

Edited May 19, 2018 by kerbiloid

[ARS]

From engineering standpoint, what's the feasibility of catamaran/ twin hull submarine and trimaran/ triple hull submarine?

[kerbiloid]

Project 941 Akula aka Typhoon was a trimaran (or pentamaran if you want), but inside a light envelope.

Spoiler

Without the envelope it would carry less water, but have greater drag.

[magnemoe]

6 hours ago, kerbiloid said:

Project 941 Akula aka Typhoon was a trimaran (or pentamaran if you want), but inside a light envelope.

  Hide contents

Without the envelope it would carry less water, but have greater drag.

Pretty nice solution, note that you need ballast tanks anyway and they are not pressurized. Looks like it has two reactors, you pretty much had to have it with this design 

It has an sauna and an pool. 
http://en.people.cn/n/2015/0701/c98649-8913866-3.html
 

Edited May 19, 2018 by magnemoe

[kerbiloid]

7 minutes ago, magnemoe said:

Pretty nice solution, note that you need ballast tanks anyway and they are not pressurized. Looks like it has two reactors, you pretty much had to have it with this design 

40% of its underwater displacement was water between the hulls.
On one hand, it has to carry this water. On another hand, after venting the ballast it had enormous buoyancy which allowed it to crash 2.5 m thick ice or to go in shallow places.

Edited May 19, 2018 by kerbiloid

[ARS]

Why steam locomotives have their boilers placed on the front section of the locomotives and the driver's cabin on the rear, unlike diesel which is placed on the middle or rear section while the driver's cabin is on the front?

[kerbiloid]

Probably because coal is behind.

[monophonic]

2 hours ago, kerbiloid said:

Probably because coal is behind.

Ultimately this, although not so much directly as because the co-operation between the engineer and the fireman is much easier when both are working in the same space. This co-operation is crucial for most efficient operation of the engine.

History of the steam locomotive is long and varied, of course. So there have been a plethora of cab forward and middle designs for various purposes. Some were more successful in their niche than others, but none replaced the traditional setup in general use.

[ChrisSpace]

How do I translate the metabolic measurement system (mLO2 h⁻¹ g−0.67) into something understandable? Say an animal has a metabolism of 3.8 mLO2 h⁻¹ g−0.67 and a mass of 90 kilograms, what's it's metabolic rate?

[tater]

 

[winged]

Few questions regarding solid fuel:

1. What are ISPs of solid motors used in various missiles? Are they as good as for solid rockets used in launch vehicles (230-260 of specific impulse at the surface)? Or maybe significantly worse?

2. What type of solid fuel was used in ABM Sprint Missile or russian Gazelle?

3. Do you know what HNIW or NGNC is? Are they some exotic types of solid fuel? I've found config for them inside RO gamedata folder with note that they're extremely expensive but didn't find any information using Google or Ignition book.

Edited May 27, 2018 by winged

[Spica]

Regarding your first question, after a little bit of poking around encyclopedia astronautica I found the following:

     http://www.astronautix.com/m/m55tx-55tu-122.html : Minuteman I ICBM first stage, Isp 237 s at sea level

     http://www.astronautix.com/s/sr19.html : The second stage of the minuteman II has a pretty high Isp, 288 seconds in vacuum.

The early versions of the Sprint ABM seem to have used a polymer bound fuel grain containing ammonium perchlorate, nitrocellulose, and small bits of zirconium metal. http://up-ship.com/blog/?p=4971

NGNC is most likely a mix of Nitroglycerin and Nitrocellulose, and HNIW is another name for CL-20. https://en.wikipedia.org/wiki/Hexanitrohexaazaisowurtzitane

[ARS]

What's the (supposed) actual advantage of gyrojet rounds compared to normal cartridge rounds? Seeing as the actual gyrojet weapon has inadequate performance (bullet starts slow and then accelerates, bullet veering off course, bad accuracy at long range but bad power at short range (it won't even harm the finger placed directly at gun barrel)). Does it even make a good weapon to substitute normal cartridge rounds?

[magnemoe]

5 hours ago, ARS said:

What's the (supposed) actual advantage of gyrojet rounds compared to normal cartridge rounds? Seeing as the actual gyrojet weapon has inadequate performance (bullet starts slow and then accelerates, bullet veering off course, bad accuracy at long range but bad power at short range (it won't even harm the finger placed directly at gun barrel)). Does it even make a good weapon to substitute normal cartridge rounds?

In short no it was not an good idea as in cool but inefficient. 
Now for larger and heavier weapons like an grenade launcher it sounds way more practical as they are recoil restricted. 
In zero-g the lack of recoil would also be useful as an normal gun would cause you to rotate. 

[kerbiloid]

1 hour ago, magnemoe said:

In zero-g the lack of recoil would also be useful as an normal gun would cause you to rotate. 

They won't rotate in zero-g

Spoiler

Akimbo in da space. 

.

[magnemoe]

1 minute ago, kerbiloid said:

They won't rotate in zero-g

  Hide contents

Akimbo in da space. 

.

In real life you would get an angular momentum pushing you upper body back and your legs forward. Not sure how much from an pistol but this would be an serious issue with an machinegun.