## Tuesday, September 22, 2015

### Venus

The second planet from the Sun, Venus is even worse for stuff than Mercury is.  First of all, the gravity is almost the same as on Earth, so that wouldn't be a problem.  Unfortunately, you would still be crushed by 1,322 PSI or 90 atmospheres of pressure at sea level, which is about the same as 900 meters below the surface of the ocean.  Handily, it's very easy to calculate approximate atmosphere pressure in sea water, since pressure in atmospheres is almost one-tenth of depth in meters, but it's not exact, so you can look at this for your pressure calculations: http://www.calctool.org/CALC/other/games/depth_press  Or this to do the calculations yourself: https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html

It seems that it would be impossible for humans to survive the pressure, but perhaps they could!  An intriguing page talks of exposure of mice to 90 atmospheres of pressure, with survival of the mice.  A couple of google searches later, I found this, however, the link to the PDF appears to be broken.  Then I found out that the article is from Science magazine, in the 5 June 1964 issue.  To download the PDF, you need to be subscribed to Science magazine, which I am not.

This is what happens to a Styrofoam cup at 2300 meters:

Probably the house would collapse from the pressure, but it would be possible to build a habitat that could withstand the pressure, like a research submarine.  Lava flows are the closest to oceans that Venus has, and there's no way that a boat could survive floating on lava.  What would happen to the plane is neatly summed up by What If, and also segues to our next problem:
Your plane would fly pretty well, except it would be on fire the whole time, and then it would stop flying, and then stop being a plane.
The other problem with Venus is the heat.  Its mean surface temperature is 735 K, hot enough to melt lead.  You could survive for a short time in another kind of Fire proximity suit if it weren't for the pressure.

However, above the clouds, they say that Venus is surprisingly like Earth, albeit a Earth with sulfuric acid, unbreathable atmosphere, and category-5 hurricane winds.  It's so much like Earth that NASA has a Venus exploration plan using airships, known as HAVOC (High Altitude Venus Operational Concept):

Conclusion: Venus is hard, but not impossible, as long as you're okay with not going to the surface.

## Saturday, September 12, 2015

### Looking at the Earth

That is the ISS HD Earth viewing experiment you see directly above.  It is a experiment to determine how quickly HD video camera image quality degrades when exposed to the space environment (mainly from cosmic ray damage) and verify the effectiveness of the design of the HDEV housing for thermal control.  The people behind the project kindly broadcast the video, which shows stunning images of Earth.

For a long time, most space photography was looking up, at the Moon, the Sun, and other astronomical objects.  Then, on Oct 24, 1946, a captured V2 was launched from New Mexico's White Sands Missile Range, with a camera taking photos every 1.5 seconds.  The camera was destroyed on landing, but the images survived.  This is the first image of Earth from space:

Since then, there have been thousands upon thousands of photos of Earth from space.
See here for some iconic ones, and see here to browse tons of photos of Earth.
Why do astronauts love to take pictures of Earth?
Something called the Overview Effect.   To learn more about it, look here, (While you're at it, look at their image-a-day service here)
Then look here:

And here.

Of course, most of this is from low Earth orbit, there are plenty of pictures from farther away:
The Blue Marble
Earthrise
The Day the Earth Smiled
And Pale Blue Dot

## Monday, September 7, 2015

### Mercury

Mercury is the closest planet to the sun, and also the smallest planet, about the size of the Moon.  It's gravity is about 38% of Earth's gravity, so if you were the world's high jump champion, you could jump 6.4 meters.  But you're probably not the world's high jump champion, so if you divide your jump height by 0.38, that's how high you could jump on Mercury.  You will probably get something like 1.2 meters, if you're between 20 and 30 years old.  Long story short: Averages are hard.

Anyway, all that means that you could dunk a basketball almost without raising the ball above your head.

So, the human, and the structures would be fine in the gravity.  Mercury has no atmosphere to speak of, so the airplane would be useless, and since there are no oceans on Mercury, the boat wouldn't be very interesting.  The house could stand in the gravity, and the lack of atmosphere wouldn't affect it, but the heat would.

The temperature:
Because of it's proximity to the sun, the temperature varies wildly between day and night, with 100 K (−173 °C; −280 °F) temperatures at night to 700 K (427 °C; 800 °F) temperatures during the day at some equatorial regions.  That's definitely too hot for most of the house, but you could survive in something like a fire proximity suit.  The house could survive if it was made out of something with a higher melting point than tin.  At night, a spacesuit would be necessary.

Mercury has been suggested as a colonization site, as it has lots of solar power, not terribly unreasonable temperatures near the poles along with possible ice deposits, and possible deposits of Helium-3.

In short, Mercury would be fairly survivable, with proper equipment.

## Friday, September 4, 2015

### Welcome the starliner!

Welcome the Starliner!

Boeing's new LEO spacecraft, previously known as "CST-100," has received a name!
The Starliner will deliver crews to and from the International Space Station (ISS) or a private space station, as a replacement for the Space Shuttle.  It can carry seven people at a time, and be reused up to ten times.  It is expected to fly to the ISS crewed for the first time in 2017.

## Wednesday, September 2, 2015

### Specific impulse

Our topic for today is another rocketry concept: Specific impulse (usually abbreviated Isp).  Basically, it's how efficient your rocket engine is.  It's defined by how far each unit of fuel moves your rocket.
Here's the formula:
$Isp equation$  Where:
• $I_{{sp}}$ is the specific impulse in meters per second
• $F_{T}$ the thrust in newtons
• ${\dot m}$ the fuel consumption in kg/s
So, Isp is how much thrust you get per unit of fuel.

If your Isp is higher, then you can get more Delta-V with the same rocket.  In the rocket equation, $v_\text{e}$ is used instead of Isp, but the concepts are the same.