TSP isn't a managed fund at all. TSP is a plan housing several index and target date funds. You could say the Lifecycle funds are "managed" because the weightings were set by a manager, but the underlying funds are index funds, so even that's a stretch. That's part of what keeps the expense ratios incredibly low.
bluedevil, I think your question though is about asset allocation. We'll assume we're only talking about your retirement assets - more about that later on. You can google "asset allocation" and find months of reading if you desire. I'll give you my OPINION. I'm not a CFA or any other credentialed anything.
As a 1Lt with a stable job and many, many more years left in your career, I'd be (and I was) very aggressive. 100% stocks. S or C fund is the only question, and I'd do a mix of both. (I get my international exposure via non-TSP funds because I want broader exposure than what you get in the I fund.) Maybe 70/30 C/S, maybe 50/50. The C is going to do better in some parts of the business cycle, the S is going to do better in others. You're better off not timing it. Read up, pick your allocation, and leave it alone. I don't like the Lifecycle funds because I think they waste space. L2050 right now has almost 10% in the G fund. In your mid-20s, I consider the G fund a waste. There's no reason to accept that low of a return when you can handle more risk.
You need to be maxing BOTH the TSP and an IRA when you're able. Preferably both of the Roth persuasion, too, because your taxable income/AGI while in the military is about as low as it'll ever be.
Now, as to your comprehensive financial strategy: Retirement is only one piece, under which you have your TSP, your IRA, eventually your 401K, etc. You also need an emergency fund, savings, checking, etc. Read up on those topics and decide how to allocate your assets across the entire spectrum.
I love talking about this stuff, but again, I'm not your advisor. If you want professional help, look for a CFA that charges by the hour. Get them to make you a plan and go from there.