"Mission Concept" vs "Mission Scenario"

Question

I am in a bit of a pickle. Currently we are designing a space mission. My boss and I do agree that the "what" and "why" needs to be defined first. However, we are in a very strong disagreement on how this is called.

I, for one, think that the "what" and "why" is encapsulated by the "Mission Concept". My Boss thinks it is called the "Mission Scenario". For me the mission scenario is the "how" and "when", my Boss thinks vice versa.

Usually I am fine with accepting definitions like that, its just names for things. However, this time I have a very hard time doing so. Mainly this is because my boss insits this is the "standard way" and "it is defined like this in ECSS". I have now read through ECSS-E-ST-10C incl. Annex A and B, ECSS-M-ST-10C and NASA's System Engineering Handbook and come to the conclusion that the Concept is what I think it is an the Scenario follows suite or can be part of the Concept (which also makes sense) and is also what I think it is. However it is not clearly stated in any of these documents. The strongest hint is a part of this definition, however still not clear.

We discussed this and he wouldn't really listen and argue that he is right. He loves standards and their process so I still considerd that I am wrong and am happy to accept his proposal of calling it "the other way around" of what I would have called it for the sake of moving forward.

However, a world would fall apart for me since I thought I understood all of this (finally after my studies). This is why I came here to hear your guys thoughts and opinions on concept vs scenario. Happy to accept this as well, however I would love to have some closure on this so I ask the hive mind here :)

I know this is oddly specific, so specially thanks to every answer :)

Answer 1

I can only answer from the European/ECSS perspective.

The various phases in mission design and implementation are defined in ECSS-M-30A Project phasing and planning. From you description it sounds you're in Phase 0 (Mission analysis/needs identification) or maybe Phase A (Feasibility). In these phases, we only talk about concepts:

Quotes from section 4.3:

Phase 0:

[...] identification of possible system concepts [...]

Phase A:

[...] exploring the various possible system concepts [...] comparing these concepts against the needs [...]

The term "scenario" is not defined in ECSS, as you found. However, a "scenario", in my day-to-day experience, includes at least a timeline and events connected to this timeline. This is a level of detail you typically do not need in Phase 0. Of course, a mission justification could include a scenario.

So, I'd say you are right and your boss is wrong, but you decide if this is a battle you want to fight.

Answer 2

The choice of words is here IMHO mostly a matter of framing the audience for your intentions, and possibly also whether looking at the big picture or looking at some details:

• A concept proposes a spacecraft with capabilities and possibly with a mission target or goal upon which is decided whether the spacecraft and mission is funded at all

• A scenario assumes the mission happening and outlines a particular or different courses of how the mission will be performed. This could discuss different start dates, fly-bys, different instrument utilization, possible targets-of-opportunity, etc. A scenario assumes a spacecraft with its capabilites and discusses its utilization.

Thus when suggesting a mission to a funding committee you include of course the concept with the description of the intended technology imployed, their technical readiness level (TRL) and following assumed work to be done and possibly also by whom. Additional to that you may want to include different mission scenarios based on possibly different assumptions or timelines found in this concept.

In your particular case, you should decide whether this semantic argument is a hill to die on for you.