Total Pageviews

Monday, September 4, 2017

Getting into orbit

Disclaimer:  I  ain't no rocked scientist.

But it seems foolish the way were are getting into orbit.  I understand why Elon Musk is going this rout.  He wants technology that is capable of landing on Mars using it's rockets. Returning rockets to earth this way, as he is doing, is a good test ground for eventually landing on mars.  But for others, who are sending payloads into orbit, it seems pretty costly and inefficient.  The problem to be overcome on Mars is that the air is so thin that it doesn't have the potential to slow down a rocket as does the earth's atmosphere.

Very likely I am wrong.  My calculus is rudimentary and I base the following on simple (high school) physics a touch of Skunk Works philosophy*

*The Skunk works  buys everything it can off the shelf and only innovate those parts of a system needed for the particular function it wants to achieve.  They are consistently within budget and beat deadlines. They have had projects such as the U2 spy plain and the stealth aircraft.

Why Calculus?  If you want to calculate how far you have gone in a car traveling at a constant velocity you just multiply velocity times time.  For instance, traveling at 50km per hour for two hours, you travel 100km.  Sending a rocket into space gets a tad more complicated.

You have a slightly decreasing gravity as you go into near earth orbit, a rapidly decreasing fuel and oxidizer load as you burn off fuel, a decreasing air resistance as you get higher  but an increasing air resistance as your speed increases.  Calculus allows you to combine  these and other constantly varying factors to ultimately work out, for instance, how much fuel you need to get a given payload into orbit.

While we are talking about complications, there are certain restrictions you have to observe.  You can't accelerate too fast or you may damage your payload (people and instruments).  You also must not achieve too great a speed too soon.  If you do, you will burn up the outer skin of the rocket.  The Black bird, for instance, cruising at an altitude of  85,000ft (16 miles)  at Mach 3 (three times the speed of sound) has it's outer skin heat up to about 300degrees C.  The only reason it survives is that it's skin is made of Titanium rather than an alloy of Aluminum.

This introduces another problem into the mix.  Sometimes it is useful to go to the extreme limit of a problem to get an instinctive feel for it.  For a rocket to get into space it needs it's energy to overcome a number of factors.  It must provide enough thrust to equal the weight of the rocket and  more is needed to accelerate the rocket.  For every kg of rocket weight it lifts by a meter, a kgm of energy is needed (9.8 joules).  More still is needed to overcome air friction.

Lets go to the extreme case and take a rocket that provides just enough thrust to hold it in position.    It is not gaining altitude.  It is expending energy to no useful purpose and the amount of energy equals the rate of energy being expended multiplied by the time it remains stationary.  From this you can see that the faster it accelerates, the less total energy it will need just to support it's weight.  The less energy that is wasted just supporting it's weight, the more energy goes into acceleration.  However the above restraints limit how fast it can accelerate.  All this means it needs more fuel.  Remember this analogy.  It will become important a little further along.

Most rocket ships use an oxidizer, often oxygen itself and a fuel which is often Hydrogen.  Already we are courting disaster.  You either have to hold these gases at very high pressure to have enough on board to do the job or at very cold temperatures so that they liquefy.  In both cases you need very special tanks that weigh a lot compared to the sort of tank that you have in your car for gasoline or diesel fuel.  The high pressures or extremely cold temperatures also cause problems.  If we could get rid of this sort of fuel and oxidizer we would be far better off.

So what is the solution.  How about this.  Take the first stage of your rocket and strap on four, off the shelf, 747 turbo-fan engines.  The PW4000 develops just under 45metric tons of force.  So four of these = a little under 180 tons.  Lets call it 150 tons to be conservative. Perhaps better still, use blackbird engines which can work at very high altitudes. In either case you are now using the air as an oxidizer just as all jet planes do and your fuel is the relatively benign jet fuel (very similar to kerosene or diesel fuel).  look at the range of these aircraft.  Just on the fuel in their wing tanks, a 747 can fly a third of the way around the globe at around 30,000ft.  Pretty impressive, no?

On second thought, there might be a third type of engine that I am not familiar with that would be better than either of these two.  The regular 747 engine is designed to work best at around 30,000ft and the Black bird engine to work at super sonic speeds.  What we need is an engine that will work at subsonic speeds at very high altitudes. How about this one.

The ram jet and the scram jet can operate at very high speeds and high altitude.  As we get even above the altitude that they can operate because of the thinness of the air, perhaps we could start to introduce some of our oxygen into the combustion chamber until ultimately, the flap on the front of the engine closes and we are a rocket.

Whatever engine you decide on, suppose that you don't have enough thrust now to send your rocket straight up.  Lets strap on a pair of wings and take off from a runway.  The shallower the angle of take off, the greater the load for a given amount of thrust.

Why the wings.  Not only do they allow you to lift payloads far greater than the thrust of the engines but also with far less fuel.  Once again an example is useful to get a feel for the problem.  Picture a 747 at cruising altitude neither gaining or loosing altitude.  The thrust it needs and hence the rate of fuel use is far less that if it turned its nose upward and just hung there on its engines.  With or without wings, you still have to lift x kgs up to y meters but the wings, to a large extent support the weight of the payload without needing this huge extra thrust just to support the weight. And you completely get around the problem of not being able to accelerate too quickly or to achieve a high speed at low altitude.

So where have we got to so far.

Basically we have a stripped down 747, possibly with a modified wing for lift at high altitude and suitable high altitude engines.  How much weight have we eliminated.  A 747 can carry 660 passengers in a one class configuration and very conservatively, each passenger weights 100kg.  That is 75kg per person plus 25kg of baggage.  As I said, this is very conservative.  The load carried is therefore 66000kg or 66 tons and we haven't even considered the freight they carry independent of their passengers and all the fittings inside the fuselage needed to accommodate their passengers.  I don't know how much this would amount to all told but it is considerable.  Probably around 100 tons for passengers, freight and all the fittings the passengers require.

So how do we carry the second stage (the first rocket stage or ram jet - scram jet stage) up to high altitude to be launched.  We have three choices.  We can sling the rocket under the plane, carry it on top the way they did with the shuttle when transporting it back to be refitted after it landed or we can carry it inside the fuselage.  The two outside options probably require some reinforcing for the contact points.  The inside option necessitates a bomb bay or an opening ceiling such as the Shuttle had.  As odd as it seems, carrying the rocket on top might be the preferred  option.

So how do we launch.  The mother ship flies toward the equator where the maximum earth rotation boost will be obtained (about 1000mph) gaining altitude as it goes.  When at maximum altitude it turns to face East so that it is traveling in the direction of the earth's rotation.  It puts on full power and does a vomit comet maneuver.  That is to say it pulls up into a parabolic curve at zero gravity or even a slight negative gravity.  At or before the peak, the second stage (first rocket stage) detaches and fires it's rockets.  The mother ship veers out of the way of it's rocket blast.

Another possibility is that the rocket fires at launch, using both fuel and oxydizer until mach 3 is reached.  At this point, the ram jet can cut in and take the rocket higher on just fuel.  Note that the launch will probably be sub sonic so the ram jet will not operate.  It needs about mach3 to operate. 

We have lifted the weight of the second stage up, say 100,000ft, gone through by far the greatest part of the atmosphere and given the second stage a speed of, 1000 miles per hour of earth rotation speed plus, say, 500miles per hour from the mother ship.    We might be able to get away with some of those off the shelf solid state rockets and further eliminate the problematic hydrogen and oxygen.  Initially, a couple of small canard nose wings might be sufficient to maintain direction.  In the vacuum of space those little nose rockets would maintain direction.  We need to achieve about 18,000 mph.  The solid state rocket shells might then be cut loose or alternatively, they could be configured on the ground to be a useful component for the construction of a space station.

The converted 747 then flies (mostly glides) back to base.  It can have another rocket attached be refueled and be back at the launch point  in a few hours.  We could probably launch 4 or 5 rockets each day this way from a single mother ship.

We need costing by professionals far more qualified than I am but it just seems to me that we could get massive payload into orbit far cheaper than we are doing today.

By the by, whatever happened to the idea of building a space station in the form of a bicycle wheel or a cylinder.  With the appropriate spin, there would be one G at the rim and the astronauts would cease to have the weakening of their muscles and the wasting away of their bones.  If you want to play around with some figures, centripital acceleration equals the square of the peripheral velocity divided by the radius of the circle.  Put this equal to 9.8m per second squared and you can work out the details of your space station.

Electric VW combi, bulli, mini-van

VW is finally going to give us the electric Combi.  Fantastic, but they must keep the faith.

The original Combi was iconic for a number of reasons.

* It was simple compared to other vans.
* It was easy to work on - easily repaired
* It was affordable
* It didn't change its styling from year to year.

It should be not only possible but really easy to produce an electric Combi that excels in all of these.  Styling is simple.  Once it is designed simply don't change it.  This is a vital factor in making a car become iconic.  It also allows better pricing.  It is expensive to re-tool your body presses each year.

Electrics by their nature are far simpler that petrol cars.  Make very very sure that everything that might have to be done on the car is very simple to do.  The engine should be removable by undoing 6 nuts and sliding in a new or reconditioned one.  Batteries should be exceedingly simple to replace (for instance when new technology results in an even better battery).  CV joints should be doable by a modestly competent home mechanic and so forth. Go over the rest of the car (exclusive of the propulsion system) and make sure every part is easy to work on.

And don't put in everything that bumps and squeaks.  We are not looking for luxury in the combi.  Just a good ride in an affordable vehicle which has great range and is inexpensive to maintain.  At the very least, make all the flash options just that.........options.

If your engineers simply can't resist a challenge than get them to work on  a way to clad the whole roof with solar cells such that they all give their full power despite not being co-linear or being partially shaded.

No one expects to be able to drive only on solar.  That is unrealistic but what a nice bonus and a way to get you out of trouble if you have ignored the charge of your battery.  It happens.

Keep the faith and you will sweep the market.   Such a car is not for everyone but many of us want to have a smaller footprint.  Many of us want a car that we are proud to drive.

And for #@%^&; sake, don't make it self driving.  We like to drive.  Besides we don't want to be spied on all the time or worse still have our vehicle hacked and therefore come under the control of  someone else.  Even worse, we don't want the various secret service organizations to be able to decide to drive our car over a cliff or into a tree.  In short, we don't want our car even to be connected to the WWW.