For Questions That Don't Merit Their Own Thread

[K^2]

On 1/12/2017 at 4:21 PM, Findthepin1 said:

So my mother made soup the other day and it got cold and she put it in the microwave to warm it up and put oregano seeds in it and when it was out of the microwave the oregano seeds had all clumped into a hexagon in the centre by themselves. What causes this?

What you saw was 2-dimensional crystal growth. Seeds floating on the surface have a bit of attraction. If nothing disturbs their movement, they will clump together forming a lattice. If you get them to move, however, they will prefer the state of increased entropy and start moving independently of each other. That's effectively a phase transition, equivalent of going from solid to gas for substances. I'm guessing, liquid was either boiling or simply moving quickly enough (stirring, convection) to cause the seeds to move about. As movement in liquid died down, it was equivalent of cooling down for the seeds, and they started to clump together.

The reason the process started from the center is that microwaves tend to heat ceramics better than fluids, despite wavelength having been selected to achieve just the opposite. So in a bowl, liquid warms up from outside and moves up and towards the center. So any clusters of seeds would float towards the center, and that's also where the lattice temperature will be the lowest. Crystals tend to grow symmetrically as it is, but in this situation it's almost a guarantee.

[55delta]

Hypothetically, if someone made a space vessel like the Space shuttle (same engines, same crew accommodations, same cargo capacity, similar thermal protection) but without provision for wheeled landing, how many, and how large would the parachutes have to be for it to land intact and safely? If retrorockets were needed, how big would they have to be?

[magnemoe]

50 minutes ago, 55delta said:

Hypothetically, if someone made a space vessel like the Space shuttle (same engines, same crew accommodations, same cargo capacity, similar thermal protection) but without provision for wheeled landing, how many, and how large would the parachutes have to be for it to land intact and safely? If retrorockets were needed, how big would they have to be?

Unless you use an para sail and landing ski like a plan for the gemini pod you can forget parachutes, speed would be too high and you would would be very vulnerable for side wind. 
You would have something like the spacex mars colonial transporter upper stage, smaller and might have an drop tank like the shuttle. Yes it would be smaller as it would only need space for the crew and an cargo bay. 

[55delta]

Quote

41 minutes ago, magnemoe said:

You would have something like the spacex mars colonial transporter upper stage, smaller and might have an drop tank like the shuttle. Yes it would be smaller as it would only need space for the crew and an cargo bay. 

 

You mean for a retro-propulsive landing? I was considering more a combination of parachutes and retrorockets, like the Soyuz capsule. Does that open up any possibilities?

[magnemoe]

47 minutes ago, 55delta said:

You mean for a retro-propulsive landing? I was considering more a combination of parachutes and retrorockets, like the Soyuz capsule. Does that open up any possibilities?

Better than pure parachute who has to be gigantic to get an acceptable landing speed for something heavy. 
Wind will still be an major issue, an powered landing let you select an landing spot, this will be hard with parachutes and you will have to compensate for wind then landing and kill horizontal speed.  
Not much of an issue with an small pod who can roll over but this will be space shuttle sized, even if fairly cone shaped it will still be high, think dc-x. 
My best bet would be to use air brakes / grind fins for control and generate drag, then an powered landing. 

One interesting idea is to have an option to separate the pressurized crew compartment in front from the engine, system and cargo hold part. Top would be lightweight, no life support or heat shield, its only suposed to be used if the ship can not land safely, problems with engines or system after deorbit or an abort as this craft would not handle an water landing, it would need an parachute but it would probably not double as an braking parachute for main ship. 
 

[Kryten]

I really doubt you could land Shuttle practically without landing gear by any method, simply because of the relatively fragile tiles covering the lower surface and the high gross mass.

[p1t1o]

It should be noted that large parachutes are surprisingly heavy. The chutes for the SRBs each weigh around 1 metric ton and are rated for around 90 tons of payload.

So, it might sound like it makes sense in a mass-for-mass way, to replace the retractable landing gear for a couple of these large parachutes, but there is a reason that we don't parachute things that often, and that is because you can only slow things down so much with chutes. To get rid of the last 10-20m/s you need to expand the chute to huge proportions, so impacts are heavy. It is less of a problem with skydivers because their mass is so comparatively low, but injury on landing is not uncommon. Space capsules have crash-seats for crew and often an extra soft-landing mechanism such as an airbag or retro rockets, plus they are not always reusable afterwards. Though even space capsules have been known to have hard landings, and a large craft like the shuttle would have a much lower strength-to-mass ratio.

So prepping the shuttle to deal with this, if it didn't actually cost more mass in the end (which you obviously dont want) it almost certainly would increase the safety risks (which you probably also do not want).

Why do they not install at least one parachute for emergency use? Because it would only be useful in a very small handful of scenarios, you could only use a chute if your speed was low enough and if you were in an appropriate altitude band.

But anyway, why bother? A parachute slows you down by aerodynamic drag, so do wings. You'd need an extra mechanism to soften the landing, the shuttle already has landing gear with hefty suspension.

 

TL;DR - why replace an aerodynamic+soft landing system with another aerodynamic+soft landing system? Especially when the first one gives you far more control over your flightpath?

[55delta]

Hmm...interesting...

Okay then, next question. This one is about the actual STS this time. I've heard the space shuttle was meant to be reusable from the initial concept. So, how did the designers originally think they were going to get their vehicle back? Was it always intended for a glide landing, or was that incorporated into the design as the scope, and size, of the design increased?

[DerekL1963]

3 hours ago, 55delta said:

So, how did the designers originally think they were going to get their vehicle back?

Which vehicle?   The Shuttle we got was the end of a nearly decade long process of R&D during which every sensible idea (and a whole raftload of insane ideas) was examined at least once.   There was never any 'original' design or vehicle, or even 'one' design or vehicle until very near the end of the process.

[Servo]

9 hours ago, 55delta said:

Hypothetically, if someone made a space vessel like the Space shuttle (same engines, same crew accommodations, same cargo capacity, similar thermal protection) but without provision for wheeled landing, how many, and how large would the parachutes have to be for it to land intact and safely? If retrorockets were needed, how big would they have to be?

*Other quote*

Hmm...interesting...

Okay then, next question. This one is about the actual STS this time. I've heard the space shuttle was meant to be reusable from the initial concept. So, how did the designers originally think they were going to get their vehicle back? Was it always intended for a glide landing, or was that incorporated into the design as the scope, and size, of the design increased?

Most of the designs involved a runway landing. I think this was mainly because the original project specs required high crossrange capability (ability to change where it lands once it hits the atmosphere). Preliminary shuttle designs are always something cool to try and build, if you're up for a challenge.

 

 

As for your question on parachutes, physics can provide the answer you need.

In order for your shuttle to have a safe landing speed of 4 m/s (at the upper bound of what Soyuz lands at), your parachute would have to sufficiently lower your terminal velocity to that speed. The terminal velocity equation is as follows:

Vt = sqrt(2mg/(Cd*p*A))

Vt = terminal velocity (4 m/s for this example)

m = mass (the shuttle massed in at 75000 kg empty)

a = gravitational acceleration (9.8m/s^2)

Cd = coefficient of drag, something inherent to every shape. For most parachutes, this number is 1.75.

p (rho) = density of air (1.2 kg/m^3)

A = cross-sectional area. This is what we're solving for.

 

A = 2mg/(Cd*p*V^2) = 43750m^2

sqrt(A/pi) = radius of the parachute = 118m across.

Not too shabby. For comparison, the Apollo CM had three chutes 17m across. That amounted to 2723m^2 parachute area.

 

If we allow a faster touchdown speed (6m/s) and a better parachute (Cd=2), the numbers change a lot:

A = 17013 m^2   which amounts to a radius 73m.

Edited January 27, 2017 by Servo

[55delta]

That answers both questions quite nicely, Thank you, Servo.

[meyerweb]

Imagine a craft carrying three satellites to be deployed into an equatorial triangle around, say, Duna.  An efficient way to get the satellites into their triangle is to have the carrier craft take up an elliptical orbit with an orbital period 4/3rds as long as the orbital period of the satellites after they’re inserted into circular orbit, with its periapsis intersecting with the satellites’ final orbit.

So if the satellites are supposed to be in an orbit with a period of 300 minutes, the carrier should assume an orbit with a period of 400 minutes.  Then, each time the carrier reaches periapsis, one satellite undocks and injects itself into a circular orbit.  Do that three times, and you get three satellites equidistant from each other around the equator.  The carrier then moves to another orbit, or deorbits, or something that will prevent it colliding with one of the satellites.

My question is: what’s the technical term for the 4/3rds orbit the carrier is on while it’s dropping off the satellites?

Edited February 3, 2017 by meyerweb

[DerekL1963]

9 hours ago, meyerweb said:

My question is: what’s the technical term for the 4/3rds orbit the carrier is on while it’s dropping off the satellites?

Resonant orbit.

[meyerweb]

3 hours ago, DerekL1963 said:

Resonant orbit.

Thank you!

[0111narwhalz]

If I left a Petri dish inside the vessel of a nuclear reactor and continuously fed it sterile agar, could the bacteria with which the dish was previously inoculated become somehow radiation-tolerant? If so, could the solutions developed by said bacteria be useful in the context of spaceflight?

[Kryten]

6 hours ago, 0111narwhalz said:

If I left a Petri dish inside the vessel of a nuclear reactor and continuously fed it sterile agar, could the bacteria with which the dish was previously inoculated become somehow radiation-tolerant? If so, could the solutions developed by said bacteria be useful in the context of spaceflight?

They would die immediately; it'd like trying to create a race of super-tough humans by shooting people in the head. 

[0111narwhalz]

14 minutes ago, Kryten said:

They would die immediately; it'd like trying to create a race of super-tough humans by shooting people in the head. 

Uhm.

Perhaps not that close to the reactor. Just a...a little shooting.

[kunok]

8 hours ago, 0111narwhalz said:

Uhm.

Perhaps not that close to the reactor. Just a...a little shooting.

Something like: this doses/distance kills everything, lets try a little far away, umm here looks like a 0,1% of them survives a couple of days, what if we make that sample to grow and reproduce and redo the process?
I'm curious as well, is this somewhat doable? We could grow a radiation resistant cianobacteries or whatever in the same way we are doing antibiotics resistant bacterias?

[0111narwhalz]

Anyone have a nuclear reactor and the requisite biological equipment?

We must apply large amounts of science.

Edited February 5, 2017 by 0111narwhalz

[JayPee]

@0111narwhalz@kunok this might be up your alley:

https://en.wikipedia.org/wiki/Atomic_gardening

[0111narwhalz]

8 minutes ago, JayPee said:

this might be up your alley:

https://en.wikipedia.org/wiki/Atomic_gardening

So how about this: A very large Petri dish, rad source in the center. It is inoculated and continuously dusted with new agar. Near the center is a dead zone. The rim is unaffected. Intermediate to this, one should see a chaos of damaged bacteria. The interface between "healthy" and "blasted to bits" should, hypothetically, move inwards if the bacteria can improve their radiation resistance, by the simple fact that there is less competition there.

[p1t1o]

@0111narwhalz

https://en.wikipedia.org/wiki/Radioresistance

https://en.wikipedia.org/wiki/Deinococcus_radiodurans

 

 

Edited February 6, 2017 by p1t1o

[Toonu]

I'm not sure what is a negative mass or how in the predictions and concepts can someone make it. Is it somewhat connected to anti-matter mass? I m now talking about negative mass and Alcubierre warp drive. 

Thanks for reply! Ave! Toonu

[ChrisSpace]

Taking into account the accelerating expansion of the universe, what's the most distant object that could be reached by a spacecraft that left Earth now at 99.999(insert lots of 9s here)999% of the speed of light?

[munlander1]

What charges are used to destroy a rocket when the roster terminates the launch?