Thursday, September 29, 2016

Planetary Protection

Planetary protection is about preventing contamination of life between planets.  This for two reasons: first, so alien planets are kept in their natural state for study, and second, so Earth is not contaminated by possible harmful extraterrestrial life.  Mostly, this consists of attempting to sterilize spacecraft to different degrees depending on what category of planetary protection mission it is, which you can read about here.  The current best method of decontamination is cooking spacecraft at high heat for a couple of days.

However, the topic of this post is what humans should do when manned spacecraft travel to Mars.  It will not be possible to keep a manned spacecraft at the same level of sterilization, just because of the humans.

There are a couple of basic options that exist.

The science option:
Life on other planets should be preserved until it has been completely studied, without any confusion over whether said life has accidentally been moved from Earth.  In theory, you could record everything about a life form, and then it would not matter what happened to it, but in practice methods for studying things will always be improving, and so you will not learn everything about it.

The survival option:
Anything that could be dangerous to humanity without providing an equal or greater benefit should be destroyed.  This is maybe a reasonable, if callous, option for microbial life, but what if the life is more complex?

The preservation option:
Nothing must be destroyed or changed.  This sounds good, however, any exploration or travel to other planets changes them, and leaving planets alone will eventually result in a disaster destroying or changing things there.

So what's the best option?  None of them.
A good analogy for this things is colors.

These are squares are completely red, green and blue.

They are unarguably colors that would be a very bad choice for, say, a living room.  And a compelling argument for any color is how bad the other two would look.  If you imagined your living room painted that green, you would think that maybe that blue wasn't so bad.  The same with the options of planetary protection.  All options, when taken to their extreme, sound bad, and the strongest argument for any one option is how terrible the other two would be taken to their extreme.

Unfortunately, none of the options are the best one.  We must proceed with a mix of these, based on what kind of life we find of Mars, if any.

Wednesday, May 18, 2016

Thrust Vector Control

I'm trying a new format for this post, sort of like a Q&A.

Q: How do rockets steer?

A: Well, in a car steering refers to both figuring out where to go (looking at the road) and the actual physical mechanism that steers the wheels and changes the direction.  Which one do you mean?

Q: The physical mechanism.

A: Since rockets spend much of their time in a vacuum, the mechanism for steering must not rely on an external force, like fins do.  There are three ways that spacecraft do this: 1) with small rockets pointing in different directions, called reaction control thrusters.  This is Apollo's reaction control thrusters:

Credit: National Air & Space Museum, Smithsonian Institution.

And here is the Apollo CSM with the thrusters installed:

By National Aeronautics and Space Administration (Apollo Lunar Surface Journal (direct link)) [Public domain], via Wikimedia Commons

These are good for moving large spacecraft, but do burn a limited supply of fuel.

2) With reaction wheels.  This is where large spinning flywheels are sped up and slowed down to rotate the spacecraft.  These are beyond the scope of this post.

3) With thrust vector control.  Thrust vector control is where you rotate the engine bell a couple of degrees, effectively making part of the engines thrust go towards rotation of the spacecraft.  That is the steering losses talked about previously on this blog.  Thrust Vector Control (TVC) is good for moving large spacecraft easily with minimal added weight.  However, it can only work while the engines are firing.

Almost all rockets use it during ascent, due to how much control authority is needed.  TVC is how seemingly unstable  rockets, like the Atlas 411 ( (Lockheed Martin))  or the Space Shuttle, both of which have a balance that changes a lot during flightl, are able to stay flying straight (of course, all Atlas variants are asymmetrical).  The Space Shuttle has an extremely large vector range, which you can see here:

The engine rotation mechanism is called a gimbal, and uses different ways of rotating the engine.  Basically, though, the engine is hinged in 2 axes above either the bell, or the entire engine.  The engine is then rotated with hydraulic or electromechanical actuators.  Now, you might notice that I only said 2 axes.  That is because you cannot provide roll control without some kind of off-center thrust.  Rockets either use multiple engines, gas generator exhaust vectoring (beyond the scope, again.), or just reaction control thrusters.

Until next time.

Sunday, April 17, 2016

Mission proposal essay

I haven't put up a post in a couple of days, due to finishing an online course.  The last assignment was a essay presenting a made-up space mission to a space agency.  I decided to publish it as a blog post.


Snow Area Measurement, Mapping, and analYsis (SAMMY)

This is a proposal for mission to launch a satellite which will gather valuable information relating to global snow condition.

Mission goals

This mission will launch a satellite to gather data about snow condition around the globe, providing important information about climate change’s effects.  

It will accurately map information about snow around the entire planet.  This will provide valuable data on snowmelt, snowpack, and the processes driving them.  With SAMMY, we can track snow area, depth, and quality, which is a highly important yardstick for global warming and extremely valuable for climate change tracking.  By gathering data on snow quality, we can learn more about climate change and the Earth’s weather patterns.  

SAMMY will use a near polar orbit to gather data over the entirety of Earth’s surface.  A polar orbit is just like an equatorial low Earth orbit, but it’s rotated 90 degrees, so every 90 minutes, when the satellite comes back to the same point on it’s orbit, the Earth has rotated below it to the south, so a new area is below the satellite. (King, 339)

Importance of this mission

Addressing climate change is a global imperative, and the measurement of snow quality is a very good way of learning about it and its effects.  

SAMMY will be able to collect data far more efficiently than local ground-based methods.  Due to its polar orbit, it can gather data about snow on a global scale, rather than in the very small, localized, areas where weather stations are.

Publishing this data will be valuable for many scientific, educational, and citizen-based entities around the world.  The data on the condition of snow will also create large benefits in areas such as: meteorology (improved weather models), snow-based recreation (increased safety), and better information for search and rescue (pinpointing where blizzards and avalanches have occurred).  

Technical challenges

The largest technical challenge will be the accuracy of the snow-monitoring measurements.  This should be surmountable by using such techniques as GPS location for the satellite, or other calibration techniques.  

Instrument technology also appears to be an issue with SAMMY.  Technology will soon be available that enable the creation of instruments that can measure snow condition from orbit.  However, this will require a relatively long development process.  To keep the budget low and time of development low, use of pre-fabricated or off-the-shelf components will be maximized.

Other options

There are other options for gathering the same data.  The most obvious one is a large array of ground based stations.  These stations could give more accurate measurement, but the largest problem with that is getting enough stations to even come close to the area SAMMY would cover.  

Another option is the use of snowfall measuring satellites.  While snowfall measuring satellites are good for meteorology, they cannot track general quality as well as SAMMY would.  

SAMMY will fill an important gap in Earth observation satellites.  

Systems engineering approach


The payload is the most important part of any space mission.  In this mission the payload will contain the space-hardened instruments used for the collection of the data.  Also required is a datahandling system, and a transmission system so the data can be used on Earth.
A Guidance, Navigation and Control (GN&C) system is absolutely required by the space environment for keeping the spacecraft on course.  An electrical subsystem is necessary for providing power to the components of the spacecraft.  Thermal control will prevent heat from building up during the daylit portion of the orbit, while heaters will prevent the spacecraft from freezing during the unlit portion of the orbit.  


The payload consists of the required instruments for gathering the location, depth, and quality of snow around the planet.  The selection of the instruments will be made in a further study.  The data on snow, accumulated by the instruments, will need processing for transmission by the datahandling system, which consists of a group of computers that turn raw data from the instruments into compressed and arranged data for transmission.  Then the processed data will be transmitted by the telecommunications system, which is primarily composed of the antenna.  The antenna will transmit in the 1-40 GHz range of all satellites.  

In a low polar orbit, atmospheric drag, gravitational forces, and debris in the form of old satellites, used upper stages, paint flecks, and many other sources create the need for a propulsion and attitude control system.  It will keep the satellite pointing in the right direction (attitude), in the correct orbit, and away from debris, which would damage or destroy the satellite.  The attitude control system will use reaction wheels, which work by speeding up or slowing down flywheels for high-accuracy, low-fuel use attitude control.

The attitude control system will be commanded by an inertial control system.  Inertial control systems work by the fact that a gyroscope will keep pointing in the same direction, regardless of location of rotation.  However, they will eventually become out of plane due to small forces applied to them over time.  A gimballed star tracker, which works by staying pointed at various reference stars will be required to correct the inertial control system (“Spacecraft Star Trackers”, 10).

The electrical subsystem will consist of a primary power source.  Solar panels will be used, and they will collect power during the sunlit portion of the orbit.  The surface area of the solar panels will be determined after the power requirements are determined.  Batteries will be used for a secondary power source during the portion of the orbit which is not sunlit.  The powerhandling system, which is a simple group of computers, will control charging of the batteries and providing conditioned power to the other systems.  

Thermal control will consist of radiators and heaters for individual instruments and systems.  The radiators are flat plates, sometimes with channels inside them for pumping fluid through them, that radiate heat away from the spacecraft in the form of infrared radiation.  The heaters keep the spacecraft warm during the extremely cold portion of the orbit with no sunlight.

Finally, the structure will consist of a either a pre-made bus, which is a pre-fabricated spacecraft platform, with everything a spacecraft needs except for the payload, or a custom structure.  The PROTEUS bus’ specifications appear to be very similar to the requirements (“PROTEUS Data Package”).

Ground segment

The ground segment will handle data collection, data processing, and spacecraft command.  
The existing network for spacecraft communication can handle data reception and spacecraft command.  The data can be processed after it’s been transmitted.  Then the data will be compiled into charts, maps, and graphs and then published.

The mission control segment of the ground segment will control all aspects of the spacecraft.  

Launch segment

There are many launch vehicles that would work for this mission.  The selection will be dictated by compatibility of the satellite with the launch vehicle’s adapter(s), capabilities of the launch vehicle, and cost.
Also to be considered is the environment inside the fairing, including the cleanliness level, noise level, axial and lateral g’s, temperature, and pressure.

Final note

The SAMMY spacecraft would provide a large benefit in many areas that are crucial to the world’s successful adaption to global temperature increase..  It would create a large return for a relatively small cost.

Thank you for reading.


Various, cited section by King, Michael Our Changing Planet. Page 339 Pub: 2007. Accessed April 

Spacecraft Star Trackers. NASA. page 10. Pub. July 1970. Accessed April 2016. URL:
Rapid III Spacecraft PROTEUS Data Package. Pub. ???? Accessed April 2016. URL:
Taylor, Travis. Introduction to Rocket Science and Engineering. CRC Press. Pub. 2009 Accessed April 2016.

Wednesday, March 9, 2016


Reentry (technically atmospheric entry) is when anything enters a atmosphere.  Specifically, reentry is when something launched from an atmosphere reenters any atmosphere.

During reentry, the air around the spacecraft is heated to plasma, due to compression and friction.  This makes for beautiful videos:

When you want a spacecraft to survive reentry, heat is the largest problem.  G-loads are a problem, but that's a function of craft aerodynamics and entry angle.

There are many ways to deal with the heat of reentry, here's a couple of the most common ones.

Ablation cooling:
This is where, effectively, you just use the heat of reentry to "ablate" or vaporize a material.  Much of the cooling effect comes from the cooler boundary layer created by the gases created from pyrolysis, or decomposition of material at high temperatures without oxygen, of the ablative material.  It was first proposed by Robert Goddard in 1920. 
The materials used for ablative cooling vary, but can be as simple as treated cork.

Heat sink cooling:
Heat sink cooling, is simply, making the heat shield out of high-thermal-conductivity materials, so that it efficiently moves and stores the heat away from the fragile payload.  This was used on the Mercury Redstone suborbital craft with a beryllium heat shield.
The space shuttle used another type of heat sink, reinforced carbon-carbon, or RCC.  The biggest problem with this method is the weight.

Radiative cooling:
The space shuttle's black tiles on the lower half of it, known as HSRI, are radiative heat shields.  They work by radiating heat back away from the shuttle very efficiently, and by not internally transferring heat efficiently.  It is so good at heat radiation and so bad at thermal conductivity that you can hold one side of a HSRI tile while heating the other side with a blowtorch and not get burned.
However, some heat always soaks through, and so the space shuttle always must be hooked up to ground cooling equipment after landing to avoid damage to the aluminum frame.

Active cooling:
This is where you circulate a cooling fluid through the heat shield, or spray a fluid onto the surface of back of a heat shield.  The complexity and weight make this less than perfect for most applications.

Transpiration cooling:
Like ablation cooling, this uses a boundary layer to insulate the payload.  However, the boundary layer in transpiration cooling is made out of a fluid injected through many small holes in the heat shield.

For more information, and a history, take a look at this ebook:
I haven't finished reading it yet, but it looks interesting.

Wednesday, February 10, 2016

Gravity turn

When you watch a rocket launch, you see that it gently tips over as it climbs.  This is because to stay in orbit, a vehicle must travel sideways, very fast.  However, it must also climb above the atmosphere.  Obviously, going straight up until you reach space, then turning 90 degrees and going into orbit is inefficient, and going sideways immediately after launch is also inefficient.  So what do rockets do?
First, there are three terms we must familiarize ourselves with: gravity losses, drag losses, and steering losses.
These term refer to things which require delta-v aside from expending delta-v just to increase your total speed in a vacuum.  So your total speed after expending all propellant would be total potential delta-v (if your rocket was going in one direction in a vacuum with no gravitational losses) minus gravity losses, drag losses, and steering losses.
Gravity losses are the delta-v expended that is just fighting against gravity, instead of speeding up the vehicle.  To imagine this, think of a rocket with a thrust to weight ratio of exactly 1, that is hovering just above the launchpad.  This rocket, in free space, could accelerate to 1,000 m/s, but, because gravity losses take up all of the potential delta-v, it's end speed is zero.
Drag losses: if your rocket expends 1,000 m/s of delta-v in a gravity-less vacuum, you end up travelling at 1,000 m/s.  However, if you put an atmosphere in that vacuum which your rocket must travel through, then drag will slow the rocket down, even as it continues to accelerate.  The difference between the total potential delta-v and your end speed is the drag losses.
Steering losses: you have a total potential delta-v of 1,000 m/s, and you expend 500 m/s going in one direction in a gravity-less vacuum, then you turn around 180 degrees and expend the remaining 500 m/s.  Your end speed is zero, because your steering losses are 1,000 m/s.
Back to gravity turns.  A gravity turn is the optimized curve from vertical to horizontal of a rocket traveling to orbit.  Because a rocket "balances" on its engines, gravity slowly pulls the front of the rocket down, which works efficiently, because less delta-v is needed for steering the rocket, and because the angle of attack (angle of the rocket to the air it's passing through) in almost zero throughout the entire ascent.  An ideal one will have a minimum of drag, gravity, and steering losses.  Turning too sharply to early will result in high steering losses, and turning too late will result in high steering losses.
Ideally there should only need to be one steering event, at the very start of the gravity turn, pitching over 5-10 degrees while the rocket is still fairly low in the atmosphere.  Then gravity should take over. 

Saturday, January 23, 2016

Jupiter and natural satellites

Continuing our exploration of the planets...
Jupiter is the fifth planet from the sun.  It is two and a half times as massive as the other planets combined.  It is not like any of the other planets we've looked at so far.  It is a gas giant, and even though some is known about the outer layers of it, for the simple fact that the conditions are so extreme that the only spacecraft that has ever explored it was only able to survive for the first 150 km of atmosphere before being crushed.

Here's what Jupiter is like as you move in towards the center:
Jupiter has a ring system, this is the first planet with rings.
The very outer layer of the atmosphere is gaseous, but steadily changes into a liquid as as pressure increases.
It is mostly made of hydrogen, but other "fun" chemicals exist, such as hydrazine (corrosive) ammonium hydrosulfide (flammable, toxic), and ammonia ice (generally poisonous and corrosive).  Wind speeds above 100 m/s are common.
As pressure increases further, the hydrogen turns into liquid metallic hydrogen, so named because it is an electrical conductor.   
Much further down is the core of Jupiter.  It is relatively small, but about 12 times heavier than Earth.  It is not know exactly what the core is made of, although it is probably rocky.

Jupiter's gravitational field is 2.54 time stronger than Earth's, and it's average temperature in the outer atmosphere is about -240 F or -151 C.  That, combined with the fact that the pressures would crush almost anything very far down at all, mean that Jupiter isn't very good for any kind of human outpost, much less anything designed for Earth.  Theoretically, some kind of floating station could be built in the very outer atmosphere.

On to the moons of Jupiter!
We'll be skipping the very small moons, because they aren't very interesting.

Jupiter's very nearest moon, Io has over 400 volcanos.  It is very geologically active because of tidal forces from Jupiter and Jupiter's moons.  It's surface is mostly plains, spotted with volcanos and mountains.  It only has traces of an atmosphere, it our stuff wouldn't react much differently than on the Moon, aside from the colder temperatures, due to being further from the Sun.
Europa has a water ice crust over a basic rocky planet.  It is likely, though, that a liquid water ocean exists below the icy crust.  In combination with it's oxygen atmosphere, it is a surprisingly good planet for humans.  Not great, or anything, since it's atmospheric pressure is 10−12 bar, compared to Earth's 1 bar.  The surface temperature at the equator is about −160 C (−260 F).  The sub-surface ocean is probably heated by tidal forces.  An undersea base on Europa would probably be possible, converting the water to oxygen and hydrogen to generate rocket fuel and breathable atmosphere.  Of course, anything from Earth would freeze without protection.
Ganymede is a large lump of icy rock.  It also may have a subsurface ocean.  It has a molten iron core and almost no atmosphere.
Callisto is, again, a large lump of icy rock with a possible subsurface ocean.  Interestingly, below the possible subsurface ocean, the rocket and ice in not stratified like in most planets/moons.  It is probably the best bet for a surface base, being far from Jupiter to minimize radiation, and geologic stability.
And finally, since this post doesn't have a video, here's some robotic falconry: