Yes, but we have good tools to solve this now. NASA has put a lot of research into designing space craft in such a way as to utilize all required mass as shielding. Furthermore SpaceXs starship that is actively being designed with lunar/Martian landings in mind and the sheer scale of this spacecraft gives you a lot of capacity to bring mass only as shielding. While this is a problem it’s absolutely a solvable one and far from the greatest hurdle to a mars mission.

This is one of the primary advantages starship will have over other lunar landers. The sheer mass of the ship will allow you to devote a significant amount of payload as primarily a radiation shelter.

Depends what you mean by make it big. Some will likely succeed and even thrive as launch companies. However launch is a particularly difficult part of the industry to succeed in. The overwhelming majority of the revenue in space is made from providing satellite services not launching them. There is a reason SpaceX is trying to break into that market. Launch is incredibly competitive and is likely to become more so as reusable rockets increase the development required to be competitive while lowering the expected revenue per launch. All of these problems are exacerbated by the sheer number of small sat providers entering the market. There just isn’t the market demand to sustain all of these providers. 1-2 maybe but there are several dozen. And almost 10 with real hardware/potential to be operational in the next year or so. From the outside it looks like that whole segment of the industry is bubble that is about to pop, and the only ones that will survive long term will be the ones that can progress beyond small launch to the medium/heavy lift as both relativity and Rocketlab are working towards.

They have long since abandoned ACES in favor of incremental upgrades to centaur such as improved performance and on orbit lifetime. These are primarily geared towards national security payloads and don’t really offer much in the way of revolutionary change.

As of now nothing, but They are working on a number of high profile contracts for both launch and in space operations for the government and private industry. In essence they are the closest thing to a competitor that SpaceX has (in terms of future potentate) as such they get included as the honorary second place. And to be perfectly honest I’m not even sure that’s wrong. In terms of existing completion SpaceX has ULA but they have shown little willingness to innovate from a tried and true method. The Vulcan is barley competitive with falcon 9, let alone starship. Likewise rocketlab is currently developing a rocket that might be superior to falcon in some metrics but likely won’t be competitive against starship. Relativity space has the same problem but is in a worse position as they haven’t launched once. So if you were looking to make an inclusive panel of representatives from various space launch companies who would you pick

I’d be willing to bet they were green onions.

Who cares to make a bet on where the booster will renter this time.

What are you a doing step Mario

The fact that they have delivered engines for ULA proves that they should be taken seriously. As they were able to develop a massive rocket engine on a more cost effective and aggressive schedule than Aerojet rocketdyne who was largely building their AR1 engine based off of Soviet designs. That alone is a huge achievement, keep in mind the complexity of a rocket engine drastically increases with scale. What rocket lab, astra, Virgin, and all the others has accomplished is impressive but it’s not nearly as challenging from a propulsion standpoint. Secondly they are included in these discussions and plans because what they are planning can actually contribute to them. Astra, virgin, relatively and all the rest would need to scale launchers by a factor of 10-100 to be able to even contribute to similar plans. Some of these companies are planning such vehicles but their development is even further behind than that of NG.

Most of the gas lost to space is hydrogen and helium. Due to its lower molar mass it is much easier for these molecules to reach escape velocity.