Friday, December 25, 2015

Kerbal Space Program AAR, The New Plan

Remember how I had said that we had enough money to finally upgrade the construction facility? That was only technically true (the best kind of true though). While we had the money to upgrade it, we lacked the money to get any use out of the new upgrade. A sad state of affairs for us, as we wouldn't be going anywhere new this time, but ah well. Earning one's worth never hurt. The selection of contracts is interesting though, and I pick out a few.

First up is another mission to save the hapless pilot of a careless private space program. Good pay, better than usual even, so what's the catch? They forwarded the details over, and it became apparent what the catch was:

Looks like they had intended on going for a Munar runby. All seemed well until on the return trip back they didn't have the fuel to re-enter the atmosphere. Normally, I'd put this up to bad rocket craftsmanship, but looking closely at the data, I realized that they had gone west instead of east.  They didn't want it known publicly that their flight plan was completely backwards.

 I wanted to go blabbing to the press at yet another failure by the private industry in the hopes of getting more contract money sent our way, but Fishman had me promise not to. Signing the contract meant we'd be stuck to silence. What I wouldn't give for the chance to send all lawyers into the sun.

Well, no time for that now. I have work to do in getting that pilot back home. I had plenty of time though, as she's a day out from a good intercept point. Rather than wasting the entire day, I have Capt. Kiwi suit up for a side mission. As well, I grabbed two other missions, one to test parts, along with a future run to Minmus. Likely we'd do it after rescuing the lost pilot, but for now the juicy advance money would come in handy.

It was the usual Aeronautics mission. Go take temperature readings somewhere in low altitude. Easy money. This one was a short flight over, just past the lower peninsula I named "Kerbea".

Capt. Kiwi and his trust flyer were soon brought out onto the runway. Easy money.

The beauty of these trips is great. We don't normally get such good pictures from our rockets. Something about too much wind pressure breaking the cameras.

Almost half an hour later, and Capt. Kiwi begins approaching the Kerbean peninsula. This marks the halfway point to his mission objective.

Another 20 minutes later and Kiwi was "busy" collecting the readings. Simple job really. I'm not sure why they wanted readings over empty water like this. Isn't the weather over land where all the interesting stuff happens? You can barely see any from here, even 11,000 m above water.

The collection goes smoothly, and Capt. Kiwi moves to begin landing. He cuts power to the engines, and dives down; he's eager to get back home. Something something religious celebration.

I warn him about the treacherous water, but he insists. It'll be fine, he says. If the plane lands on hard ground, why couldn't it handle a soft wet landing?

Final approach, he's slowed down as much as he can. Splashdown imminent.

Why doesn't anyone listen to me? Kiwi's craft hits the water with enough force to rupture the tanks. launching him up into the air again and destroying much of the craft. Luckily for him, we heavily reinforce our crew compartments.

He lands safely a short distance away. It cost us some money in damaged parts, but maybe we'll get it back in advertising money. The people do love a good explosion, especially if it is because of someone's silly decision.

Wednesday, December 23, 2015

Kerbal Space Program AAR, Ship Design Explanation

While working on the plans for the next mission (which would be a doozy) Wixit the engineer came to me with a straightforward question: "How do you design rockets?" Given his ample time at base with not much else to do after his promotion, he had had plenty of time to study up on actual engineering. I was certainly busy, but my interest in getting work done was competing heavily with my interest in talking. I do so love to talk.

Ah, what the hell. Missing a bit of work wouldn't hurt anyone. We would be waiting a day for that rescue attempt anyway. I pulled out my charts and sat him down. Class was in session.

The first important bit of information involves explaining the interface. In the bottom right we have our current mass and size values and their limits, along with any warnings we might have. The limits are based off of our infrastructure. Size and mass were dependent on our launch pad, while the number of parts is based off of the construction facility. Always make sure to take these numbers into account when designing your craft.

On the left hand side we have our parts list. Parts are separated by function. Additionally, the parts greyed out require an additional purchase cost for us to use. In the center is the craft we're currently constructing. On the bottom left is the cost of the rocket so far, along with buttons for center of lift, center of mass, and center of thrust. There is also a button for where objects are placed along the edges, and if you want more than one of the same object to be placed symmetrically around the area.

That explained, the next part is to figure out the design of your rocket. First step is to determine your mission: the reason for the craft to exist, sans any concern about actual rocket equipment. For this example, lets say our mission is a trip into low Munar orbit, carrying along Science! equipment and a full Kerbonaut group. Put that together, optimally placing everything within the rocket, rather than on the sides so as to reduce drag and worry about it burning off. Make sure to place the sturdiest piece of equipment on the bottom.

Next, put up any extra considerations that aren't "Rocket"such as batteries and communications. If we want communications, we'll need batteries to fuel them, so we add some of both as well. Keep in mind that the command pod comes with a small amount of energy storage and uses some energy to move the ship. Unless you add solar panels, the only way to get more energy is to run the liquid-fuel rockets. Don't run out of energy.

The next step involves noting down and adding up the dV requirements of your mission. If you're unsure of what I mean by dV and other rocket considerations, I've written up an explanation before on this matter here. This step does involve calculations, although you can often just wing it if you're familiar with the values.You can also calculate your own values, but handy guides like this map are always nice to use. It's easiest to start from the last one and work your way up. Add on an extra percentage for mishaps and pilot errors. 10-20% for most should be fine. Don't add on trips that we'll use aerobraking for, like the last leg back to Kerbin.
Chart from the linked page

Using our chart, we're going to low Munar orbit and back, so that means our order goes (Counting backwards remember): 3400 (aerobraked), 860, 310  (cut both in half because we're only getting into a very ellipical orbit), 310, 860 (partially aerobraked), 3400 (We can roughly split this into 1400 m/s atmosphere and 2000 m/s orbit). Add them up for our total dV needed, along with the extra dV for pilot error, and we get 5,400 m/s of dV needed.

The next step is to decide where the stages go. Good times to split are when you have a lot of unneeded mass hanging on, or when conditions change and you want different engines. In our case, our rocket has three good stage points. Kerbal ground to Kerbal orbital height is a good one, because of massive changes in conditions. We don't have to worry about atmosphere, nor is thrust such a concern by that point, so it makes sense to ditch part of the craft there. The second good timing is on the last leg, where we're aerobraking down to Kerbal. We don't want to drag the leftover rocket section, because we can't properly shield it. Depending on the specific parts available to you, splitting up that middle section into two could probably be a good idea, but we can't because we're limited to 30 parts in our craft.

Now that we have our requirements, we work our way down and fill in the rockets. We start with our last stage, which contains the mission payload and which only aerobrakes. Aerobraking is straightforward for us, we just add a heat shield, along with a parachute for the last leg of the journey so we can land safely. There are various calculations you can do to make sure we have enough heat shield and parachutes for the trip down, but we'll skip those for this. Finally, add on a explosive to start the stage onto the bottom, and we have our last stage done. Mark the mass of this stage.

We move on to the next stage. This one has a rocket portion, so we want to select the engine for our tasks and add enough fuel. When choosing an engine, look for three things: Thrust, Isp, and size. We want an engine that's the right size for the rest of our rocket. Too big and we're wasting fuel lifting  up the mass of the engine. Too small means not enough thrust, which is bad. We need enough thrust to do the job, which will vary on the job we're doing. For this stage, we're limited by getting into orbit quick enough before we fall back down, so we do want some thrust, but we're mostly concerned about the Isp.

For now, we'll use this engine. It has good Isp, though not great, along with good thrust. It should work fine for our purposes. Next we add fuel, of which we need approximately 3,800 m/s worth of it. What we're looking to calculate is the mass ratio of our rocket, basically (mass of the rocket when full) / (mass of the rocket when empty of fuel). We find our required mass ratio by doing e^(dV/(Isp*9.81). Plugging in our numbers gets a result of ~3.3. ~30.3% of our mass is rocket, the rest is fuel. Assuming we have weightless fuel tanks, we'd need 9.7t of fuel. Sadly, they are not, and so we need 1/8th of our fuel mass in fuel tank mass. Effectively, we come out to needing 1.75 more tons of tank mass, giving us 14t of fuel, and requiring 13.7t of fuel. We've got only a bit of fuel remaining for additional pilot mishaps beyond the projected 10%.

Our final stage requires only ~1,540m/s of fuel, though it is in atmosphere where rockets tend to perform less well than in a vacuum. Additionally, we want to worry about thrust a lot in this section. Ideally, when you're in a thick atmosphere like that found on Kerbin's surface, you want about 2 g's of acceleration. More than that and your wasting fuel fighting air resistance. Less than that and you're wasting fuel fighting the planet's gravity. When you're looking for high thrust and big parts, your best bet is always the solid-fuel rocket boosters. Here's the one we'll use:

We calculate our mass ratio again, but this time using the atmosphere value, and come to a mass ratio of ~2.5. Four of these boosters should do the trick, but we'll add a fourth on just in case. Our rocket isn't as aerodynamic as I'd like, and it's always good to have extra fuel if we need it. Don't forget to make every part as aerodynamic as possible. Small rounded caps on the tops of our engines are quite literally worth their weight in black gold.

This leaves us with our first stage massing in at 38.3t. Even though it has relatively little dV in it, carrying the rest of the rocket is hard work.

Now, what you should do Wixit is evaluate different scenarios. See what happens when you have missions that require more dV. See what happens when you add stages, and see where the breakpoint is between having more stages compared to fewer. What would a single stage rocket to the Mun look like?

I've got to get back to work. Enjoy your homework. Those contracts won't finish themselves.

Wednesday, December 16, 2015

Kerbal Space Program AAR, Mun Tourism

Our last mission had made good money, but we weren't earning enough. Not nearly enough. I had plans for this space program, and for those plans we would need some upgrades. Now I was going to look under every nook and cranny I could find for us to make the money we needed. Luckily, our recent upgrades to the administration building meant we could take on more contracts. We could hold up to 7 now, though only 5 were of any worth.

Three Kerbals booked flights with us to go into orbit around the Mun. One VIP pulled some connections to come up cheap, but the others were paying full price. Good money, but there was more we could do.
The scientists down in the caverns wanted some scientific information from orbit around both the Mun and Kerbin. Specifically, they wanted us to take atmospheric pressure readings from orbit. Of course, there wasn't any pressure there, but it's not like they were spending their own money. Ah well, more for us, we'd put it to good use.
Lastly, a high paying customer wanted something more symbolic. He wanted us to put a flag down on the Mun. Normally, this'd be problematic, because we didn't have near the facilities to land a rocket down on the Mun. Good for us though, our star pilot Ms. Health was itching for a vacation. And where better to vacation than on the Mun herself? Sure, she'd have to use her jetpack for the final bit, but it should have enough delta-vee for her to land safely if we did enough of the work getting her there.

She'd be alone up there for a good amount of time, but all the better. Who wouldn't want to spend a year away from all Kerbal contact? So much less crazy.

Her replacement would be the rescued pilot Hermes. We offered him a better salary, and assured him that all our rockets came with parachutes. Given his the reputation of his name for his failed mission bankrupting the private rocket company that had sent him up, he'd need a new name. Fishman the lawyer gave him one; Stamasd Kerman. I suspect he used some cheap name generation software, but ah well. It'd work out.
The two pilots Ms. Health and Stamasd suited up, along with our three tourists: Melanne, Doodfen, and Buzz. The new rocket is based off The Munner rocket, and would have more fuel, along with some extra crew capacity. A real tourist contraption.
The launch schedule would look similar to our last Munar trip. Things would only change once we were in close orbit around the Mun. Stamasd would be the pilot for the entire trip, with Ms. Health looking over his shoulder to make sure everything was going smoothly, at least until she was dropped off.
Everything went according to plan to get into orbit. Same as before, orbit around the Mun wasn't too hard. Landing though was expensive. Similar to anywhere else, if you want to land safely, you need to kill your excess speed. For nearly the same amount of delta-v that it took to get here from Kerbin's orbit, we'd be able to land. That's a lot of fuel. Now you see why we used parachutes and heat shields when landing back on Kerbin.

That single heat shield allows us to ride a hot cushion of compressed air to eliminate some 1600 m/s, leaving wind resistance and the parachute to kill the remaining 1600m/s. Here, we were balking at losing a mere 800 m/s.

The beauty of rocket mechanics means that overall rocket science didn't matter. Only the ratio of fuel to mass and your efficiency did. Ms. Health has a tiny amount of fuel on her, but that fuel would go a long way. She has about 600 m/s worth of fuel all by herself. The rocket arrives at the low point, and burns against the orbit, just enough for Ms. Health to safely land.

The rocket's still moving at 500 m/s. But that was all she'd need to land.
She leaves the rocket, and boosts off to give the rocket a wide berth. Once she was clear, Stamasd fired the engines to get back into orbit around the Mun. His journey here would be like the last orbit. But Health's trip down would be interesting.

Health's rocketpack had a lot of fuel, but not much thrust. She had to start immediately if she wanted to slow down in time. Things did not go quite as planned. By accident, she clipped the side of the crater, dazing her and preventing her from controlling her flight as planned. It would be a rough ride down.

(Sidenote: I didn't realize ahead of time just how much time would be taken up by the maneuver to get both the rocket into orbit and Ms. Health safely down. I had no idea that Kerbals could hit that hard and still survive. In the future I'll likely try to be a little higher up)

But, eventually she landed. Apparently she enjoyed the crazy ride down. Mun sledding she called it. She couldn't help but look back up at Kerbin and feel something deep inside her.

Everything well with Ms. Health, Stamasd put the rocket on a trek home. This would be simple and straightforward.

Wave goodbye for now to Ms. Health, we'd be back for her...eventually.

And a successful splash down. They had all returned safely, minus one vacationer.
This was easily our biggest haul yet. One mission for more than 300,000 spesos, along with a healthy amount of Science!. Best still, we had enough to upgrade our manufacturing area. Now we'd be able to build some real rockets. And maybe someday go back for Ms. Health.

PS. Full disclosure: I needed to add a bit of fuel to the rocket to make it work. Likely could have done it with the amount of fuel I had given great piloting and more practice, but this episode is taking long enough as is.

Friday, December 11, 2015

Kerbal Space Program AAR, The Rescue

After that big mission, we had some good news and some bad news. The bad news was we had learned just how bad our facilities were for sending missions throughout space. If we wanted to do more, we'd need to upgrade them heavily, and that would cost money we didn't have just yet. The good news was, others saw how well we were doing and figured they could set up private companies to take some of our success. It's much cheaper when you don't have to do all the initial legwork to get started, and they were eager to get started. Good for us though that they're really bad at it anyway, and we'd profit off their mistakes.

Our first new mission involves rescuing a poor pilot who was stranded in orbit. An overeager company had decided to try for an orbit as their first mission. All had gone well until they were making the final checks for re-entry. Apparently they had forgotten to put any parachutes on the craft, and so coming back down would be suicide. Really, who does something that silly? As Capt. Kiwi will tell you, parachutes are the most important part of any rocket.
They didn't have the equipment to rendezvous with the stranded pilot, which is where we came in.  Along the way, we signed on a tourist to go up with us. We had the room anyway.
In order to get started, it was time for some more improvements to the facilities. The tracking center was the first to get upgraded. The facility received better equipment, mainly in the form of advanced computing hardware we called "calculators" that would let us calculate farther out how our orbits would look, even with multiple orbital bodies.
Mission control would also get upgraded. We bought a very expensive whiteboard that we could use to make plans ahead of time. It's amazing what proper planning can do for a mission. We'd also have room for more contracts at one time, if we could find any others that were worth taking.

Ms. Health and our tourist suited up for their mission, using a variant of the Spacer rocket series.
The new rocket came with more fuel, and a new scientific invention that would enable us to record the atmospheric pressure at that location. Part of our new study into aerodynamics and working with the air instead of against it.
It was time to launch. Our target was ahead of us and already in orbit. Our first order of business would be to launch into an orbit of our own, matched up as closely to theirs as we could.
Here you can see our wonderful new upgrades in action. The blue line is our orbit, the yellow line our target's orbit. The orange and purple markers mark our next two closest intercepts. The orbit wasn't as close as I'd like, but it was close enough. The problem was our target was very far ahead of us in the orbit, we'd have to catch up to make our rescue. Now came the complicated part.

On Kerbin, if we wanted to catch up to someone we'd speed up towards them until we caught up to them, then slow down to match speeds. In space, the same maneuver would be highly inefficient - too inefficient for our limited fuel reserves. This is because, if you'll recall, speeding up widens our orbit, while slowing down shrinks it. Speeding up to them would throw us off. We'd have to do things a little differently.

Our plan is to speed up, enlarging the orbit. For each time we went around, we'd make the trip faster than them, decreasing the distance between us. Do this enough times, and we'd get close enough for a rendezvous. Then we'd slow down to match speeds.
Here we were in our faster orbit. Now it was time to wait. A few rounds around the planet, and we were coming much closer with each passing orbit. Next we slowed down to match orbits closer; we didn't want to start pulling ahead of them.
The difference in our orbits was slight. We'd only catch up some 6 km each orbit, but we'd catch up. In the meantime, the eggheads wanted us to test the atmosphere in space.
 We confirm what we had already known: there is no atmospheric pressure in space, because it's a vacuum. At least the new science gizmo works.

Finally, we found ourselves only a mere kilometer away, with a 34.4 m/s (77mph) difference in speeds. While we could match speeds with our rocket if we wanted, we chose instead to have the stranded pilot do all the work. His small rocketpack was more precise than our unwieldy rocket.

He stepped off into the void. His little rocket pack contained a surprising amount of delta-vee. It was useless on Kerbin, as it wouldn't generate near enough thrust for lift-off, but here it'd allow him to travel the kilometer difference and match our speeds with no problem. Space is weird.
Final approach to the Space 4. He overshot it a tad, but what can you expect from a newbie?
On board and ready to go. All that was left was the smooth reentry. Which Ms. Health could do with no problems. It helped that we brought a parachute.

Home sweet home, with a nice chunk of change for us. Mission successful.