How cheap are low-tech(panther) spaceplanes?

[GoSlash27]

15 hours ago, Abastro said:

Refueling? Ingenious! So you can reuse the whole plane over and over? I should have opened Panther!

Abastro,

 That's kind of the point of SSTO spaceplanes; the only cost is the fuel... theoretically.

 As a practical matter, the R&D and cost to build are higher than a comparable disposable lifter, which raises the risk of using them. If you lose one during a mission, it will erase the savings you might've seen.

 I found (back in the day) that Panther based spaceplanes weren't worth the risk and effort. Not because of the Panther itself, but because of the other tech that's available at the time. Too many "puzzle pieces" for a good spaceplane still missing.
 Moreover, spaceplanes aren't very adaptable for mission roles. They restrict the size and shape of their payload in ways that vertical lifters don't and are sensitive to changes in CoM, which makes them a PITA to use as cargo haulers. This being the case, it's not really worth the time, cost, and effort to develop a spaceplane unless you plan on using it regularly. I basically use spaceplanes as crew taxi or tankers, Both of these roles presuppose either a space station or orbital construction. Neither is going on when the Panther is unlocked because critical pieces for those operations are also missing.

 By the time you develop the tech to do things that would make spaceplanes useful and viable, you've also unlocked better engines than the Panther.

Best,
-Slashy

Edited April 21, 2017 by GoSlash27

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5 hours ago, GoSlash27 said:

As a practical matter, the R&D and cost to build are higher than a comparable disposable lifter, which raises the risk of using them. If you lose one during a mission, it will erase the savings you might've seen.

Right, hence get the spaceplane to space only one time and use it over and over again. It costs less for its own mass, and it's possible to pack lots of dv there while it might be impossible with rocket with second level VAB due to the 140t limit.

[GoSlash27]

18 minutes ago, Abastro said:

Right, hence get the spaceplane to space only one time and use it over and over again. It costs less for its own mass, and it's possible to pack lots of dv there while it might be impossible with rocket with second level VAB due to the 140t limit.

Abastro,

 I must be misunderstanding what you're talking about. Get it to space only one time and use it over and over again... to do what?

Scratchin' mah head,
-Slashy

[Reusables]

1 hour ago, GoSlash27 said:

To do what?

Crew transportation, and science scraping missions. It can haul cargo as well if it has a docking port aligned to the central line.

[GoSlash27]

1 minute ago, Abastro said:

Crew transportation, and science scraping missions. It can haul cargo as well if it has a docking port aligned to the central line.

Sorry, I need more info. I should rephrase. To travel where?

 

[Reusables]

12 minutes ago, GoSlash27 said:

Sorry, I need more info. I should rephrase. To travel where?

Primarily, exploring all the Mun&Minmus biomes. It can be done in short duration.

Also it can easily go interplanetary as well when refueled; @Wanderfound's spaceplane has 5.6km/s when fully refueled, which I think is sufficient to get to Jool and back.

[Spricigo]

But, if you can put a plane in orbit and refuel,  you can also put a rocket and refuel.  

After reaching orbit jet engines and wings are dead weight if your destination is an airless celestial body. For this purpose the spaceplane being the tanker makes more sense. 

[GoSlash27]

Just now, Abastro said:

Primarily, exploring all the Mun&Minmus biomes. It can be done in short duration.

Also it can easily go interplanetary as well when refueled; @Wanderfound's spaceplane has 5.6km/s when fully refueled, which I think is sufficient to get to Jool and back.

Abastro,

 Okay. This is what I was afraid of. Bad idea.

 A spaceplane is like one of those "duck- boats" from WWII; it's a truck that can float or a boat that can drive (depending on how you look at it), but it's not a good truck or a good boat. It's strength is that it bridges the gap between both because it can do both.
 Likewise, a spaceplane does *not* make a good spaceship. It's hauling around wings, air- breathing engines, control surfaces, landing gear, and structure to make it fly well in atmosphere that never gets used in space. It's more expensive, less efficient, and more cumbersome for the job of "spaceship" than a purpose- designed spaceship would be.

 This is coming from a guy who's a big proponent and fan of spaceplanes: They are really good at their assigned mission and it's an important one... but don't confuse that role with one that something else can do better.

 A spaceplane gets your people or supplies from a point on the surface of an atmospheric planet to low orbit and back again. It is not the best option for anything other than that. If you need a plane, build a plane and leave off the stuff that helps it be a spaceship. If you need a ship, build a ship and leave off the stuff that helps it fly. The spaceplane is what you use to connect crew and supplies between the two.

Best,
-Slashy

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53 minutes ago, GoSlash27 said:

 Likewise, a spaceplane does *not* make a good spaceship. It's hauling around wings, air- breathing engines, control surfaces, landing gear, and structure to make it fly well in atmosphere that never gets used in space. It's more expensive, less efficient, and more cumbersome for the job of "spaceship" than a purpose- designed spaceship would be.

Can't agree more. But when there is hard limit of 140t (before 3 tier VAB), so there is certain mass limit of the spaceship. Meanwhile, spaceplanes can get to orbit as SSTO relatively easily, so it's kinda like 'heavy spaceship in one go'.

Now I realized that pretty much everything can be done with 140t. But mun landing with mobile lab can still be pushing. In addition, big spaceplane is also a mobile station.

(Forget about crew transport, I think I won't need something like 20 passenger spaceplane)

I don't think wing/landing gear weighs much relative to the whole mass. (Or isn't it?)

... And there are airbreathing engines. What about decoupling it once on orbit, and recover it later?

57 minutes ago, Spricigo said:

But, if you can put a plane in orbit and refuel,  you can also put a rocket and refuel.  

But rocket lacks LF storage, so they most likely have less dv. My calculation shows that fuel cost more with chemical engines even with 0.6 kerbin TWR and 1500m/s. Reliable mun lander should have more than that, doesn't it?

[Wanderfound]

1 hour ago, GoSlash27 said:

A spaceplane gets your people or supplies from a point on the surface of an atmospheric planet to low orbit and back again. It is not the best option for anything other than that. If you need a plane, build a plane and leave off the stuff that helps it be a spaceship. If you need a ship, build a ship and leave off the stuff that helps it fly. The spaceplane is what you use to connect crew and supplies between the two.

From a strict efficiency POV, yeah.

OTOH, there's more to life than efficiency. Given an orbital refuelling depot, that last model of the Minmus Panther I posted could easily clean out every biome on the Mun or Minmus in a single trip, and would work well for Duna and Laythe too.

But you could probably achieve the same goals a smidge cheaper if you instead used a cargo SSTO to haul a dedicated space vessel into orbit and bring it back down again (although the size restrictions of Mk2 cargo bays add some complication to that).

Taking your wings to Eeloo and back is fun, but all it gets you is style points.

[Spricigo]

2 hours ago, Abastro said:

But rocket lacks LF storage, so they most likely have less dv. My calculation shows that fuel cost more with chemical engines even with 0.6 kerbin TWR and 1500m/s. Reliable mun lander should have more than that, doesn't it?

I think you missed the point.  Consider we both designed very similar SSTO spaceplane,  about the same mass,  same engines, same fuel capacity, same wing area... Both have barely enough deltaV to reach orbit but can be refuelled. 

However mine is designed to get rid of jets and wings just before reaching orbit.  Guess which one will have higher deltaV and TWR after refuelling.

You may argue that recovery can make your design cheaper,  however this only is true if I didn't use mine enough to archive a better economy. 

 

 

Edited April 22, 2017 by Spricigo

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7 minutes ago, Spricigo said:

I think you missed the point.  Consider we both designed very similar SSTO spaceplane,  about the same mass,  same engines, same fuel capacity, same wing area... Both have barely enough deltaV to reach orbit but can be refuelled. 

However mine is designed to get rid of jets and wings just before reaching orbit.  Guess which one will have higher deltaV and TWR after refuelling.

You may argue that recovery can make your design cheaper,  however this only is true if I didn't use mine enough to archive a better economy.

Hm, that's right.

It's just that it doesn't work in my case, where the goal is not dispose any parts intentionally. (Except for heatshields, separators and fairing)

[Spricigo]

1 hour ago, Abastro said:

Hm, that's right.

It's just that it doesn't work in my case, where the goal is not dispose any parts intentionally. (Except for heatshields, separators and fairing)

This only means you want to separate and recovery the spaceplane while I don't care* if it burn/crash. Your compromise it's to design the spaceplane to be recovered while mine it's to accept the cost of using the plane only once. 

 

*for the sake of the example given. 

[GoSlash27]

6 hours ago, Abastro said:

But when there is hard limit of 140t (before 3 tier VAB), so there is certain mass limit of the spaceship.

Abastro,

 I haven't had any problem with a 140t pad limit; it's actually very generous. If you use the ship as it's own transstage to orbit, you can save a whole lot of weight. You also have the option of orbital construction and fueling. Plus, you don't need to take the entire ship down to the surface and back at the destination. If you use these techniques, the pad limit doesn't hinder your mass in orbit.

6 hours ago, Abastro said:

Meanwhile, spaceplanes can get to orbit as SSTO relatively easily, so it's kinda like 'heavy spaceship in one go'.

Not so much with Panthers, though. They peter out at a relatively low top speed and altitude, forcing you to use rockets to produce more of the DV to orbit. Your payload fractions wind up being in the same ballpark as chemical rocket lifters with the added disadvantage that a lot of the "payload" is actually airplane.

Best,
-Slashy

 

[GoSlash27]

7 hours ago, Abastro said:

But rocket lacks LF storage, so they most likely have less dv. My calculation shows that fuel cost more with chemical engines even with 0.6 kerbin TWR and 1500m/s.

Nah. Nobody said you have to launch with full tanks. Using mid- career tech, you can put 24 tonnes into orbit with a 140t pad limit. That payload can be whatever you want/ have access to. Crew quarters, lab, couplers, empty fuel tanks...

Let's say you use a simple 2 stage Twin Boar/ Skipper arrangement. The Twin Boar can lift up to 55 tonnes within the pad limit to the requisite 1,800 m/sec DV and initial 1.4 sea level t/w. Stage 2 becomes your dedicated spaceship, partially- fueled at launch, and capable of producing 1,700 m/sec DV before it runs dry. When it arrives in orbit, it weighs 24 tonnes.

Now... if we refuel it in orbit to make use of all the empty tanks, we could use that skipper to generate 4,400 m/sec DV to 14 tonnes of payload at 0.5g. That's a massive amount of DV; adequate to get you the Mun, Minmus, Duna, Ike, or Gilly. 14 tonnes would be your guidance, lab, landers, fuel for your landers,crew quarters, etc. This ship would weigh 123 tonnes when fully refueled in orbit.

You could go even more crazy with a pair of Poodles and strip-mine the entire Joolian system, but this ship will soon become obsolete as better tech becomes unlocked.

Best,
-Slashy

Edited April 22, 2017 by GoSlash27

[Reusables]

3 hours ago, GoSlash27 said:

empty fuel tanks...

Forgot about that! So I can launch something heavier with the tanks empty.

Though..

3 hours ago, GoSlash27 said:

Stage 2 becomes your dedicated spaceship,

I think it's simply inefficient. The second stage needs good amount of TWR which is unnecessary for spaceships. Also it has to be aerodynamic enough. (It has less mass)

And Nuke is better than chemical engines if it's reused again and again. It takes less fuel cost in most case, and slight increase of payload mass won't impact the performance.

 

I was considering mobile science lab with science experiments will weigh some mass, and landing it is needed to gain 10% science bonus. Though it won't be problem for spaceships launched without fuel(Thus max dry mass is 25t in my case).

[GoSlash27]

1 hour ago, Abastro said:

I think it's simply inefficient. The second stage needs good amount of TWR which is unnecessary for spaceships.

Abastro,

 I usually design my upper stages with 0.7 t/w and my interplanetary stages with 0.5. In this case, the upper stage would be able to generate it's .5g when fully loaded and 1.2G when partially fueled.

1 hour ago, Abastro said:

Also it has to be aerodynamic enough. (It has less mass)

Not as aerodynamic as an airplane

1 hour ago, Abastro said:

And Nuke is better than chemical engines if it's reused again and again. It takes less fuel cost in most case, and slight increase of payload mass won't impact the performance.

True, but I was under the assumption you didn't have nukes yet since you were contemplating unlocking Panthers. If you have nuke upper stages, you can take the same approach as I outlined above. Personally... I'd consider how many times I'd be using this ship. After the first mission, I'd have so much tech unlocked that I could easily build much better ships.

Best,
-Slashy

Edited April 22, 2017 by GoSlash27

[GoSlash27]

I built and flew a couple examples of what can be accomplished using tier 2 conventional rockets within the 140t limit.

Example 1 is a triple Poodle design with a pair of strap-on Skippers.

This design would get over 5km/sec DV without landers and a minimum .56g when fully fueled.

Example 2 is what I was talking about earlier; series Twin-boar/ Skipper stack.

This design can achieve 4,700 m/sec at a minimum t/w of .62g unencumbered.

Either design would get you to a lot of bodies with landers; probably more than you would wish to use them for once the tech becomes obsolete.

Best,
-Slashy

 

[Spricigo]

Ok,, there is an example of what Im proposing. Notice that its far from fully developed and I designed it mostly because I can and because  I liked.

notice that is a crude and inefficient design. Ignore the design itself, what I want to present its the concept.

[Reusables]

6 hours ago, GoSlash27 said:

I usually design my upper stages with 0.7 t/w and my interplanetary stages with 0.5. In this case, the upper stage would be able to generate it's .5g when fully loaded and 1.2G when partially fueled.

I design mine 0.4 TWR, usually I don't bother with it much. 0.7 TWR is too big for that, and 0.4TWR for circularization is usually not enough.

6 hours ago, GoSlash27 said:

Not as aerodynamic as an airplane

I forgot to mention that 'spaceplane' has relatively less mass. But I got your point, one usually don't need that kind of mass.

6 hours ago, GoSlash27 said:

If you have nuke upper stages, you can take the same approach as I outlined above.

Nuke & Panther could make great combination for long-range spaceplane. It's great for giant spaceships in 140t limit, providing lots of payload mass. It's just too big for usual applications.

6 hours ago, GoSlash27 said:

After the first mission, I'd have so much tech unlocked that I could easily build much better ships.

The problem on hard career is usually funds for upgrading buildings, it takes lots of time and effort. Especially, that R&D building takes a lot to upgrade to 3 tier. so I can't have much options with it. And I want to do it in relatively short ingame time.

 

Besides, I don't think there's much to replace pre-existing parts after unlocking nuke. Those in higher tech which are useful to me are only Gravioli & Refinery, Relay dish and Docking port Sr  & Structural parts. Other parts looks like cosmetic bits for me. The two prior ones usually need ships for its own niche, so the only thing matter is big structural parts for bigger station. Even then previois station can dock to the new ones with normal docking port. (Also it's not bad to have more stations, I think)

Personally, many techs just look obsolete, e.g. precision propulsion. (those radial engines... ;-P)

 

 

@Spricigo, is it about disposable middle stage? I can't exactly get the idea. Disposing empty fuel tanks didn't save much in my experience.

Edited April 22, 2017 by Reusables
Daneither! Merged!

[Spricigo]

2 hours ago, Abastro said:

@Spricigo, is it about disposable middle stage? I can't exactly get the idea. Disposing empty fuel tanks didn't save much in my experience.

 

No. That is me avoiding to fix a case of CoM behind CoD after I used all that fuel.

The idea its to reach the orbit with a SSTO spaceplane, but bring the plane back rigth back while the spaceship go further.

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16 minutes ago, Spricigo said:

The idea its to reach the orbit with a SSTO spaceplane, but bring the plane back rigth back while the spaceship go further.

But in the case, it's hard to match CoL and CoM. That's fundamental problem of the design, and it diminishes the performance. Also it's just barely better than reusable rockets, I guess..

[Spricigo]

37 minutes ago, Abastro said:

But in the case, it's hard to match CoL and CoM. That's fundamental problem of the design, and it diminishes the performance. Also it's just barely better than reusable rockets, I guess..

 

Actually more often my problem its with thrust misalignment generating too much torque.

[Reusables]

1 minute ago, Spricigo said:

Actually more often my problem its with thrust misalignment generating too much torque.

Did you placed the engines without symmetry? Or you mean the number of engines?

[GoSlash27]

A further refinement of the Skipper/ Poodle arrangement:

6,100 m/sec DV when refuelled, .32g minimum acceleration.

Of course, the DV can be dialed back in exchange for additional cargo, but as you can see there's simply no way that SSTO spaceplanes can hope to compete with vertical launchers for interplanetary exploration, even with the 140t weight restriction.

Best,
-Slashy