2.5m rockets

[Kryxal]

My first tourist-capable craft has the initial capsule, 1.25m bay, crew cabin, and heatshield, in that order.  It's lighter than the 2.5m capsule and works well with 1.25m stuff, plus you can make some use of body lift when you can afford to veer off pure retrograde.

[Benjamin Kerman]

4 hours ago, GoSlash27 said:

Delay,

 Here's an example of a launcher for your mission:

It has 2,000 m/sec DV on orbit and the full ablator. It's designed to be cheap, so total cost at launch is $26,000.

Best,
-Slashy

Why do you have liquid fuel tanks above the SRBs?

[Spricigo]

54 minutes ago, Benjamin Kerman said:

Why do you have liquid fuel tanks above the SRBs?

the liquid engine uses it (there is external fuel ducts linking it to central tank)

 

[Benjamin Kerman]

3 minutes ago, Spricigo said:

the liquid engine uses it (there is external fuel ducts linking it to central tank)

 

To me, that doesn't make any sense unless you configure the tanks to empty right before/after the SRBs burn out, to remove the excess weight.

[Spricigo]

1 minute ago, Benjamin Kerman said:

To me, that doesn't make any sense unless you configure the tanks to empty right before/after the SRBs burn out, to remove the excess weight.

exactly the intended purprose

[Benjamin Kerman]

2 hours ago, Spricigo said:

exactly the intended purprose

So the tanks are not connected to each other, but to the center?

[Spricigo]

16 minutes ago, Benjamin Kerman said:

So the tanks are not connected to each other, but to the center?

exactly.

 

[GoSlash27]

3 hours ago, Spricigo said:

exactly.

 

Actually, the tanks are connected to each other and then the core asparagus- style. The SRBs are jettisoned in pairs, and their tanks drain just before that occurs. Once all 3 SRB/ drop tank stages are jettisoned, the core is left full.

Best,
-Slashy

Edited January 26, 2017 by GoSlash27

[Benjamin Kerman]

2 hours ago, GoSlash27 said:

Actually, the tanks are connected to each other and then the core asparagus- style. The SRBs are jettisoned in pairs, and their tanks drain just before that occurs. Once all 3 SRB/ drop tank stages are jettisoned, the core is left full.

Best,
-Slashy

So I assume that the SRBs only fire in pairs also?

[Spricigo]

@GoSlash27 sorry about my imprecise answer early.  Intended to point that the small tanks are linked to the core and not just to each other . 

Actually,  considering all technical details,  the best way to understand your design its to download the craf and launch it. The same way the best way to understand a painting it's to look at it. 

[GoSlash27]

45 minutes ago, Benjamin Kerman said:

So I assume that the SRBs only fire in pairs also?

Benjamin Kerman,

 No, all SRBs and the core stage all fire simultaneously. The SRBs generate 1G of acceleration in total, while the core stage generates about .25G initially and all steering control. The earliest stages are throttled higher, and the later stages are throttled down to act as sustainers. By the time the boosters and drop tanks are jettisoned, the core stage is generating about .5g to the remaining mass.

 The entire lifter is balanced to shed boosters and tanks as it goes to keep acceleration within reasonable bounds to avoid aerodynamic instability and heating problems.

 This is all stuff I've already balanced, so all the end user needs to do is pile on the payload and whatever propulsion they deem necessary to circularize and complete the mission.

Best,
-Slashy

 

4 minutes ago, Spricigo said:

@GoSlash27 sorry about my imprecise answer early.  Intended to point that the small tanks are linked to the core and not just to each other . 

Actually,  considering all technical details,  the best way to understand your design its to download the craf and launch it. The same way the best way to understand a painting it's to look at it. 

^ This. The easiest way to understand how the whole system works is to download, pile on a payload, launch it, and observe it in action.

Best,
-Slashy

[Benjamin Kerman]

Ok, thank you for the clarification @GoSlash27! 

 

[Delay]

Another question I have: As of now, I can only calculate dV when:

A: The craft is in orbit, so at 0gs,

B: There's only one engine running

How do I calculate dV when "fighting" against gravity (my guess is to devide by TWR) and with more than one engine with more than one specific impulses (my guess is to take the average of all engines)?

[FullMetalMachinist]

1 hour ago, Delay said:

A: The craft is in orbit, so at 0gs,

Not sure what you mean here. The dV equation is the same no matter what your current situation is. The only thing that might effect it is the presence of an atmosphere, which reduces the Isp of the engine. 

1 hour ago, Delay said:

B: There's only one engine running

To get dV when you have multiple engines of the same kind is the same as when there's just one. If you have multiple different types of engines then it gets a little more complicated. You need to use the weighted average for thrust and Isp, then use those numbers for the dV equation. I'll admit I don't know the math well enough to quote it to you, but I know @Red Iron Crown does. 

[Benjamin Kerman]

1 hour ago, Delay said:

Another question I have: As of now, I can only calculate dV when:

A: The craft is in orbit, so at 0gs,

B: There's only one engine running

How do I calculate dV when "fighting" against gravity (my guess is to devide by TWR) and with more than one engine with more than one specific impulses (my guess is to take the average of all engines)?

Take a look at this thread: 

 

[Spricigo]

1 minute ago, Delay said:

How do I calculate dV when "fighting" against gravity (my guess is to devide by TWR) and with more than one engine with more than one specific impulses (my guess is to take the average of all engines)?

With tons of patience.

 

seriously now:

Its simple an application of Newton's 2nd and 3th Laws of motion...the complex part its to evaluate each factor (drag coefficient, speed, mass, direction of movement...).

[Delay]

6 minutes ago, FullMetalMachinist said:

1 hour ago, Delay said:

A: The craft is in orbit, so at 0gs,

Not sure what you mean here

The craft is in a stable orbit around a celestial body, and therefore not affected by anything other than gravity, which is comparable to 0g.

And I'm pretty sure that the dV you get for an orbit is no the same as under, say, 100m/s² of gravity.

[FullMetalMachinist]

4 minutes ago, Delay said:

The craft is in a stable orbit around a celestial body, and therefore not affected by anything other than gravity, which is comparable to 0g.

And I'm pretty sure that the dV you get for an orbit is no the same as under, say, 100m/s² of gravity.

Ah, you're talking about gravity losses. 

Strictly speaking, the tsiolkovsky rocket equation doesn't take that into account. A ship will have the same dV no matter what it's local gravity is. As a practical matter, if a ship has 1000 m/s dV but only 1.1 thrust-to-weight ratio, then no it's not going to get up to 1000 m/s. 

As for figuring that out purely by mathematical means, it's pretty non-trivial. But like you said, it only comes into play when you're climbing a celestial body's gravity well. This is why dV maps are extremely useful. You calculate your dV based on vacuum numbers, and the map tells you how much it takes to get to low orbit. 

[Benjamin Kerman]

18 minutes ago, Delay said:

The craft is in a stable orbit around a celestial body, and therefore not affected by anything other than gravity, which is comparable to 0g.

And I'm pretty sure that the dV you get for an orbit is no the same as under, say, 100m/s² of gravity.

The only reason for this is because you need to overcome the gravity of the body to get into orbit. As a famous quote says: "Once you get to orbit, you're halfway to anywhere." And the only reason that you might get less dV is because of the lower Isp of the engines in atmosphere. 

[Spricigo]

another way to put what @FullMetalMachinistjust said:

Tsiolkovsky roquet equation only gives deltaV from engines, there is still the gravity's deltaV and Drag's deltaV.

 

[Zeiss Ikon]

On 1/25/2017 at 4:40 AM, Sharpy said:

Forget Skipper. It's too strong and inefficient for low-gravity worlds, and too weak for Kerbin.

Orange tank or two, and Twin Boar or Mainsail go SSTO with a good 15 ton payload. Poodle is great for travel in space and landing on low-gravity bodies until you unlock nukes (and later once you want to go cheap, or with large unwieldy payload that won't neatly fit in 1.25m fairing).

 

This!  I have a simple Twin Boar booster with 8 Vernor RCS thrusters that will SSTO with 16 T on top of the 2.5-1.25 adapter.  Put another way, it will orbit two basic upper stages, each with Mk. 1 Command Pod, T25 stack mono tank, 8 RCS quads, two 1.25 m decouplers, two blue radial parachutes, one docking port (on the nose of the Mk. 1), 80 size tank, and Reliant engine, and still leave enough fuel in the booster to deorbit the whole stack.  P.S. Don't do this; you will kill one pilot if you deorbit the stack as a unit; don't attempt to fly reentry on two missions at once...