How do you get the engineer to tell you the delta v?

[Bug_]

It was hinted at in this tweet that engineers would be able to give readings: https://twitter.com/Maxmaps/status/564909904557649920

But I do not seem to be able to figure out where to read the number if you have an engineer in the vessel, does anyone know where to find the number in the game?

Edited June 1, 2015 by Bug_

[RocketPropelledGiraffe]

You don't - at the moment. I understand that the delta-v readout was delayed to one of the next updates.

If you want to get the information with a mod, try Kerbal Engineer.

[Bug_]

You don't - at the moment. I understand that the delta-v readout was delayed to one of the next updates.

If you want to get the information with a mod, try Kerbal Engineer.

Oh ok, so wait for an update I shall.

[Murph]

Oh ok, so wait for an update I shall.

For now, just install the Kerbal Engineer Redux, like I'd guess 99% of people that spend much time playing KSP.

You'll likely have a long wait for it from Squad, as I doubt it will be in 1.0.3. The big 1.1 update will be months in the future, as it includes porting/rewriting the game for Unity 5 (from everything that I've read, it really is more like porting it to a new platform, or rewriting it (sure, plenty can be reused, of course), not just an upgrade and fix a few things broken by the upgrade).

[Space Peanut]

It could be the side effect of some mod I have installed but this map screen "burn time to 0 m/s" info is pretty useful!

[Harry Rhodan]

"burn time to 0 m/s"

That seems to be not delta v but the time you'd need with your given acceleration to completely cancel your current velocity. That's not useful at all because it disregards that your acceleration will go up while you burn fuel.

[Bug_]

When you put an engineer in your vessel, the remaining delta v should be in that info box.

The formula is pretty simple, all you need is the mass of your vessel, m_0, the amount and type of fuel you have left, f, and the isp of all your engines. Assuming all engines are the same isp, the formula is just (for the example of units of liquid fuel + ox = f):

delta v = (9.81) * (isp) * ln(m_0 / (m_0 - 0.005*f))

[MathmoRichard]

I'll never understand why the 9.81 is there. If it had any relevance it was left on the launchpad. We should all measure ∆v in m/s.

[Ferdoni]

You also can use the app called Delta-V on Playstore. It helps me a lot with delta V calculations.

[Red Iron Crown]

I'll never understand why the 9.81 is there. If it had any relevance it was left on the launchpad. We should all measure ∆v in m/s.

We do, that equation delivers results in m/s. I think you mean we should use exhaust velocity (m/s) rather than specific impulse (s) for it, and you'd have a good point. The idea behind using 9.81m/s^2 to convert between them is historical: Both SI and Imperial systems use the second as a base unit, so it makes it easy for engineers and scientists used to either system to use the same figure. G₀ was used as the constant to convert them because it is a dimensionally correct one that everyone would have memorized.

[MathmoRichard]

We do, that equation delivers results in m/s. I think you mean we should use exhaust velocity (m/s) rather than specific impulse (s) for it, and you'd have a good point. The idea behind using 9.81m/s^2 to convert between them is historical: Both SI and Imperial systems use the second as a base unit, so it makes it easy for engineers and scientists used to either system to use the same figure. G₀ was used as the constant to convert them because it is a dimensionally correct one that everyone would have memorized.

Ahhh I see. Although I get the impression that the second interpretation of "specific impulse" is exhaust velocity?

Imperial is archaic IMO and silly IMO.

[Red Iron Crown]

Specific impulse is linearly proportional to exhaust velocity, it's just multiplied by a constant for convenience. I think it was a result of the postwar US space program having Germans who were used to SI and Americans who were used to Imperial, I've seen Apollo-era delta-V charts and nonograms using ft/sec instead of the m/s we're more used to.

[MathmoRichard]

It melts my mind to think that the entire Apollo program was imperial. They had the pain of measuring in silly units like pounds. Maybe it helps if you're used to it, but they still had to deal with non-decimal regimes in their working.

[OhioBob]

It melts my mind to think that the entire Apollo program was imperial. They had the pain of measuring in silly units like pounds. Maybe it helps if you're used to it, but they still had to deal with non-decimal regimes in their working.

Imperial units are easy if that's what you used your entire life.

[SanderB]

It's not so hard to convert between the two, either.

[Bug_]

We do, that equation delivers results in m/s. I think you mean we should use exhaust velocity (m/s) rather than specific impulse (s) for it, and you'd have a good point. The idea behind using 9.81m/s^2 to convert between them is historical: Both SI and Imperial systems use the second as a base unit, so it makes it easy for engineers and scientists used to either system to use the same figure. G₀ was used as the constant to convert them because it is a dimensionally correct one that everyone would have memorized.

Actually from what Scott Manley explained there's a very practical reason for putting ISP in seconds: you can let G_0 be 9.81 m/s/s, or 32ft/s/s. This way there is no confusion if you see specific impulse without a unit attached. Just multiply it by whichever one you want to get deltaV in ft/s or m/s.

[OhioBob]

I_sp is the ratio of the thrust (measured in N or lb) to the flow rate of the weight ejected (N/s or lb/s), standardized to earth gravity (g_o). The units of force cancel out and we're left with seconds. Multiplying I_sp by g_o gives effective exhaust gas velocity (m/s or ft/s). Multiplying effective exhaust gas velocity by the mass flow rate (kg/s or slug/s) gives thrust (N or lb).

[Orbital Vagabond]

Imperial units are easy if that's what you used your entire life.

Not really, I grew up using Imperial units my whole life, strongly prefer SI because it's easier. Especially in astrodynamics/physics for no reason other than SI uses distinct units for force/weight (Newtons) and mass (kg), where as the lbs are used for both in imperial.

[Orbital Vagabond]

It's not so hard to convert between the two, either.

Yeah, but it's another step.

[OhioBob]

SI uses distinct units for force/weight (Newtons) and mass (kg), were as the lbs are used for both in imperial.

That's not true if you use imperial units correctly. The base unit of mass in imperial units is the slug. You just have to get into the habit of converting pounds-mass (or tons, or kips, or ounces, or whatever unit you're given) into slugs. Once that is done, solving a problem in imperial units is no different than solving it in SI units.

The only thing I find inherently easier about SI it that units are in powers of 10. It's much easier to convert metric tons into kilograms than it is to convert imperial tons into slugs.

The one thing that I do have a major gripe about when working with imperial units is that often an equation is modified to include the pound-mass to slug conversion. This is done so that pounds-mass can be entered directly into the equation without first converting to slugs. I think this is a really bad practice that leads to bad habits and a misunderstanding of how to properly use imperial units. People need to be taught that the proper unit of mass when solving problems in imperial units in the slug, no exceptions. Once that becomes engrained into your thought process, imperial units are easy.

[Orbital Vagabond]

That's not true if you use imperial units correctly. The base unit of mass in imperial units is the slug. You just have to get into the habit of converting pounds-mass (or tons, or kips, or ounces, or whatever unit you're given) into slugs. Once that is done, solving a problem in imperial units is no different than solving it in SI units.

The only thing I find inherently easier about SI it that units are in powers of 10. It's much easier to convert metric tons into kilograms than it is to convert imperial tons into slugs.

The one thing that I do have a major gripe about when working with imperial units is that often an equation is modified to include the pound-mass to slug conversion. This is done so that pounds-mass can be entered directly into the equation without first converting to slugs. I think this is a really bad practice that leads to bad habits and a misunderstanding of how to properly use imperial units. People need to be taught that the proper unit of mass when solving problems in imperial units in the slug, no exceptions. Once that becomes engrained into your thought process, imperial units are easy.

I feel like this whole post just made my point...

[OhioBob]

I feel like this whole post just made my point...

How so? Either system requires proper training and good habits. Most of the confusion with imperial units is the result of poor training and habits. That has nothing to do with the system of units itself. Using meters, newtons and kilograms is no different than using feet, pounds and slugs. Just different names for the same thing.

[Orbital Vagabond]

How so? Either system requires proper training and good habits. Most of the confusion with imperial units is the result of poor training and habits. That has nothing to do with the system of units itself. Using meters, newtons and kilograms is no different than using feet, pounds and slugs. Just different names for the same thing.

Okay... I'm gonna preface this post with a few points. First, I really appreciate your website, it's a fantastic resource I use ton. I have tons of respect for you, and I know you know your stuff. I hope it's clear my posts are not intended to be condescending, belittling, etc. I have respect for you knowledge and understanding of the field. Second, I'm not looking for a fight on this; I've lurked on these forums for a long time, and I've seen things go really south really quick. Finally, I'm not even looking for a debate: I'm going to state my reasons for my opinion and leave it alone.

That said, I think SI is vastly superior to the Imperial system because...

1) What the frak is a slug?

I've never heard of the unit "slug". Now, on it's face that may not mean much, lots of people don't know lots of things. However, I have two doctorates, and while both are in the life sciences, I've still spent enough time in science to think that should qualify as kinda weird. This speaks to the fact that there are lots of cryptic, uncommon, and otherwise bizarre units in the Imperial system. This issue is so uncommon in SI I don't think it's hyperbole to state it doesn't exist. For mass, everything is a [x]gram; For length, everything is an [X]meter. Once you know the set of units, and the set of prefixes, you know it all. The closest this comes to being an issue is KSP is the "ton" unit.

It's a metric ton, same as a Megagram. I can understand that unit of mass immediately.

2) Is it a ton or a ton?

In the Imperial system, the nomenclature is a mess. You have to differentiate "short" tons from "long" tons, and that doesn't even touch metric tons, but that's SI... ish. Same issue for ounces: You've got fluid ounces mass/weight ounces, and troy ounces...

Just... C'mon!

3) I've only got so much brain power

In your post, you listed... *checks* 5 measures of mass? Slugs, pounds-mass, kips (?), tons, and ounces? To go directly between these, I'd need to memorize 15 separate conversions, many of which need a lot of digits for accuracy (3 or more). The option is to put everything into one unit, which is extremely inconvenient when nothing is given to you in that unit to start with.

Conversions in SI mean moving a decimal point.

That's it. I can remember that.

3A) So 9 ounces is 0.625 lbs? or 0.63 lbs? or 0.6 lbs?

Precision in a decimal numerical system is way easier when [practically] all the units are related to each other on a base 10 scale. There simply is no round off error. The Imperial system almost never uses conversions that are multiples of 10, which can cause some serious issues with precision when you're applying multiple conversions in series. Avoidable(ish) with computers, but for mental math and estimation, its a needless source of error.

This is really a subpoint of 3 and you mentioned it in the post, but it bears repeating.

4) Hybrid Units

I'm out of clever titles. In the Imperial system, it's common to report quantities in two additive values, e.g. 5 lbs 6 oz. Yes, I know how to deal with it, but the point is I have to deal with it. This is never convention in SI/metric.

I think that's it. You can chalk all this up to "poor training and habits", but those are very large and very real issues in the real world. The SI is simple and straight-forward because it was designed to be simple and straight forward, and is one of the few examples where a rational and intentional design produced such a system. I think it's a shame to not use it in place of the Imperial "system", which has, been cobbled together from a multitude of sources and disciplines, many of which are now obsolete.

Again, just my opinion with supporting points for why I think it's quantitatively inaccurate to say Imperial is "just different names for the same things." The way in which I thought your response post supported my point was that you had to bring "oh, if you're doing it right" and "people need to be taught appropriately," and you did because the Imperial system is not as easy to use as the SI system. It takes more experience and training to use than the SI system, and offers no benefits to the SI system. IMO, it's hard to use the SI system wrong and I can't imagine having to write a post that starts with "if you're using the SI system correctly".

Edited June 4, 2015 by Orbital Vagabond

[SanderB]

Converting between units is like riding a bike or a language, if you learn it young it's easy otherwise it's something that will - for most - always require effort and feel cumbersome.

[OhioBob]

Orbital Vagabond,

I'll grant you that the units in the SI system are more intuitive and easier to learn, but that's not what I was talking about. The point I was making was about problem solving. I'm assuming that a person is already familiar with the particular units that are customary in his/her particular field or industry. In that case it is no more difficult to solve a problem in imperial units than it is in SI units.

Each system has base units, which are typically what you use in problem solving. In SI the base units are meter (length), kilogram (mass), and second (time). Force is a derived unit, the Newton. In the imperial system the base units are foot (length), pound (force), and second (time). Mass is a derived unit, the slug. That is really all you need to know. If you are given a quantity in other units, you just have to convert it to the base units. Although there are many different units in the imperial system, the number that a person has to become familiar with in normal practice with is rather few. And if imperial units are what you work with every day, the units become second nature.