For Less Money Too!

[Rocket In My Pocket]

On 11/19/2017 at 9:15 AM, Plusck said:

At the end of the day, the only "real" relative advantage that the mk1-2 has going for it is partcount.

And how!

To get a similar stat line you'd need to build something like this; which is 11 parts!

• Command pod+Crew cabin for 3 person capacity.
• Monoprop tank for 30 total units of storage.
• Extra battery for 150 total units of EC storage.
• 2 Reaction wheels for 15 total torque.
• A wing part for added lifting surface we are missing compared to the Mk1-2.
• Several RCS balls for a comparable 50m/s impact tolerance. (The real Mk1-2 is 45m/s, closest I could get without adding excess weight.)

And...we're still missing about 200k of heat tolerance, and the ability to remote control probes. Also, it's ugly as all sin. It is however, still lighter though!

Edited November 21, 2017 by Rocket In My Pocket

[Spricigo]

3 hours ago, Rocket In My Pocket said:

• A wing part for added lifting surface we are missing compared to the Mk1-2.
• Several RCS balls for a comparable 50m/s impact tolerance. (The real Mk1-2 is 45m/s, closest I could get without adding excess weight.)

And...we're still missing about 200k of heat tolerance, and the ability to remote control probes. Also, it's ugly as all sin. It is however, still lighter though!

Why not just put everything inside a fairing(not staged)?  And why not use only one bigger RW if the torque is necessary? 

Anyway, as mentioned above, the question is not how to provide the same capacities to other setups, the question is if those capacities will be necessary to begin with.

[Rocket In My Pocket]

17 hours ago, Spricigo said:

Why not just put everything inside a fairing(not staged)?  And why not use only one bigger RW if the torque is necessary? 

Anyway, as mentioned above, the question is not how to provide the same capacities to other setups, the question is if those capacities will be necessary to begin with.

A fairing would have got in the way of the picture, The next sized wheel gives 15, command pod already has 5, that makes 20. Needed 15 total for Mk1-2 parity.

I'm not disagreeing, just making an exaggerated example of some of the pro's and con's of the Mk1-2. You'll notice I pointed out that this ridiculous contraption of 11 parts is still half the weight of the Mk1-2.

The intent was more for humor than for practical discussion. I'm certainly not making the argument that the Mk1-2's weight is justified by it's stats, I mean; it weighs more than the Mk3 for Jeb's sake!

Edited November 22, 2017 by Rocket In My Pocket

[Corona688]

By popular request they added a three-man pod with splendid durability.  Then they had to jack its weight up until "re-entry without parachute" stopped being the smartest option.

[IWanttobeEVA]

Once I get the Mk1-2 and the Mainsail in career mode it becomes the work horse of my space program. 

1) Rescue missions are so much easier without having to have Kerbals go on space walks to get the pilot back in the command seat. I could use a probe core here, but I usually forget about it until Jeb is kicking it in the passenger module somewhere with no other pilots on board. 

2) I'm not much of a fan of the Jr. docking port. The Mk1-2 with the regular docking port on the top is my preferred docking vechile for space stations and landers. A Mk1-2 in Mürar orbit with a lander can for multiple missions can run so many different types of contracts that these missions are always super-profitable and they more than pay for the mission. 

[wumpus]

You're looking at the wrong numbers.  The mark 1 capsule + crew cabin weighs 1.84 tons.  The mark 1-2 capsule weighs 4.12 tons.  It would make sense to pay thousands more for the mark 1+crew cabin for the chance  to cut your payload mass by more than half.  Expect the resulting rocket (made by the mark1+crew cabin) to cost easily less than half the final cost of the mark1-2 based system.

And the other players aren't kidding about not sweating this too hard.  You can miss too much of the game [guilty] if you burn out by trying to make ideal recovery systems (if you must recover, add the mods to make it take less time).

[Zeiss Ikon]

4 hours ago, wumpus said:

You're looking at the wrong numbers.  The mark 1 capsule + crew cabin weighs 1.84 tons.  The mark 1-2 capsule weighs 4.12 tons.  It would make sense to pay thousands more for the mark 1+crew cabin for the chance  to cut your payload mass by more than half.  Expect the resulting rocket (made by the mark1+crew cabin) to cost easily less than half the final cost of the mark1-2 based system.

One major problem with the Mk. 1 + Crew Cabin -- in my experience, during reentry it will never slow down enough for the parachutes to indicated "safe" to deploy.  You either have to change the default "when safe" setting and hope the canopies don't shred, or have some additional means (extra weight, extra funds) to slow down after the hot part of reentry is done.  Turning the stack sideways isn't it, BTW -- that stack is stable-ish in heat shield forward, and really stable in command pod forward, but you won't have enough torque in just the command pod to keep it from going pod-forward if you turn it more than a few degrees from heat shield forward.

Any science instruments on the outside are prone to burn off for any reentry hotter than LKO, too -- and if you add a Service Bay, you're adding cost and mass and making the stack less stable in heat shield forward -- i.e. more prone to tumble when tumbling could mean burning up.  With the Mk. 1-2, external instruments are better protected, and you can mount a Service Bay on the nose if you won't need a docking clamp there.

[Spricigo]

2 hours ago, Zeiss Ikon said:

One major problem with the Mk. 1 + Crew Cabin -- in my experience, during reentry it will never slow down enough for the parachutes to indicated "safe" to deploy. 

That issue is easy to solve, just put the crew cabin on top of the command pod, not bellow. Even if you add an adapter is still much cheaper and lighter than a Mk1-2. 

 

2 hours ago, Zeiss Ikon said:

With the Mk. 1-2, external instruments are better protected, and you can mount a Service Bay on the nose if you won't need a docking clamp there.

Or even if you need a docking port, just use the other attachment node. But that is a moot point, what can be added to Mk1-2 can be added to pod+cabin (barring part count issues).

 

[OrbitalBuzzsaw]

While the Mk1 + Mk1 PC combo is cheaper, it has all the stability of an elephant on a beach ball without an oversized heatshield, which eliminates the advantage of being able to easily fit onto cheaper 1.25 metre class rockets.

[Spricigo]

25 minutes ago, OrbitalBuzzsaw said:

While the Mk1 + Mk1 PC combo is cheaper, it has all the stability of an elephant on a beach ball without an oversized heatshield, which eliminates the advantage of being able to easily fit onto cheaper 1.25 metre class rockets.

As explained in the post right before your, just put the beach ball on top of the elephant.

Really, how hard can rocket science be anyway?

 

[Plusck]

3 hours ago, Zeiss Ikon said:

One major problem with the Mk. 1 + Crew Cabin -- in my experience, during reentry it will never slow down enough for the parachutes to indicated "safe" to deploy.  You either have to change the default "when safe" setting and hope the canopies don't shred, or have some additional means (extra weight, extra funds) to slow down after the hot part of reentry is done.  Turning the stack sideways isn't it, BTW -- that stack is stable-ish in heat shield forward, and really stable in command pod forward, but you won't have enough torque in just the command pod to keep it from going pod-forward if you turn it more than a few degrees from heat shield forward.

I find it odd that a few people have mentioned problems stability or slowing on re-entry with mk1 + crew cabin + heat shield.

Are you using FAR?

I've never had a problem with stability after getting the first "retrograde hold" capable probe core.

And I've never had problems with slowing either - a 30-32 km Pe for re-entry works just fine each time. I set my chutes to open at 0.23-0.25 pressure, which means between 8000 and 9000 metres, and the combo never has a problem. I generally reduce ablator to about 40-80 units, btw, if that changes anything (unless going further than Eve/Duna).

The only time I've had a problem with slowing has been on suborbital hops, or coming in from LKO when impatient and reducing Pe to well under Kerbin's surface.

Edited November 28, 2017 by Plusck

[Zeiss Ikon]

19 hours ago, Plusck said:

The only time I've had a problem with slowing has been on suborbital hops, or coming in from LKO when impatient and reducing Pe to well under Kerbin's surface.

Aha!  After my experience with this setup on early-career suborbital tourist flights, I never tried it at higher speeds/altitudes.  If it won't slow down from 800 m/s, what would make me think it'll slow down from 2300+ m/s?  A more horizontal reentry, however, could bleed off more speed high up and avoid a high vertical velocity component.

No, I'm not using FAR, but again, my experience with the combo was at lowish speeds, finding it wasn't terrifically stable even as it failed to slow below 300 m/s high enough to avoid "splashed down hard" results.

[Plusck]

21 minutes ago, Zeiss Ikon said:

Aha!  After my experience with this setup on early-career suborbital tourist flights, I never tried it at higher speeds/altitudes.  If it won't slow down from 800 m/s, what would make me think it'll slow down from 2300+ m/s?  A more horizontal reentry, however, could bleed off more speed high up and avoid a high vertical velocity component.

The short answer is: Mythbusters got it wrong in that "bullet drop" experiment. They failed at physics and their experiment wasn't sensitive enough (or wasn't set up correctly) to show how.

Basically, drag is proportional to the square of velocity.

If you drop something vertically, gravity accelerates it and drag limits the acceleration until it reaches terminal velocity.

If you fire something very fast (far above terminal velocity) in a straight line, gravity will likewise try to accelerate it downwards. However, from one instant to the next, that vertical acceleration is being dampened by the drag force squared which includes that vertical component. Therefore, your fast-moving projectile cannot accelerate downwards as much as a slow-moving one.

Sounds counter-intuitive, but it's the reason why a fast re-entry to a 30km Pe gives you plenty of time to slow down to parachute speeds. By the time you've reached 30km, Pe is well under the surface of Kerbin but you're still going far faster than terminal velocity, so you'll take much longer to hit the ground than if you had simply stopped and dropped from wherever your Ap is.

 

Still not convinced? Consider two ships. One dropping vertically at terminal velocity (which we'll call 300m/s), and the other (for the sake of a 3-4-5 triangle) with an added horizontal component of 400 m/s giving 500 m/s total.

For the ship falling vertically, drag exactly equals gravity (by definition since it's terminal velocity). Drag force is (some constant x) * v² and therefore at this precise instant it is 90000x and is equal to the force needed to accelerate our craft upwards by 10 m/s², counteracting gravity.

However, if we compare to our ship which also has horizontal velocity, drag force is 250000x. Therefore, since acceleration is directly proportional to force (divided by mass, which is constant here), our acceleration is 25/9 * 10 = 27.77 m/s directly retrograde. Since this is a 3-4-5 triangle, the upwards acceleration is therefore 27.77/5*3 = 16.66 m/s. 

At these speeds, we can approximate and say that one second later, our vertically-dropping ship will fall by 300m. The angled one will travel a total of 486m (500+¹/₂at² = 500-14m) but will only drop by (300+¹/₂(10-16.7)) 296.7 m...

Of course, when the vertical component of velocity is much lower and the thing you are firing has low drag (like a bullet), the effect is less significant. Easy to miss over a distance of 100m or so. Not so easy to miss when you're dropping 70km down from orbit.

[Spricigo]

13 minutes ago, Plusck said:

Physics

Another point: if your periapsis is above the surface, by definition, you're missing ther ground. You actually need to slowdown to go down.

[Plusck]

1 hour ago, Spricigo said:

Another point: if your periapsis is above the surface, by definition, you're missing ther ground. You actually need to slowdown to go down.

I intended to cover that when I said that at 30km "you'll take much longer to hit the ground than if you had simply stopped and dropped from wherever your Ap is".

Coming in fast for a 30km Pe, when you're actually at 30km then Pe is already far under the surface, and Ap might well be somewhere around the 70km mark.
Now, if you'd actually stopped and dropped from 70km, Ap would now be much lower (due to drag slowing your descent) but you'd be heading far faster towards the ground because your retrograde drag would not not be trumping gravity like it does when you are going fast.