Hi, I've found an alternative "work around" if you can't get the other suggestions to work - and doesn't involve any cheats: (and apologies if someone has already suggested this and I've missed it!)
1. Place a rocket somewhere in your lot
2. Build a fence around it (leave a bit of space to allow for sims to walk around in it - hint hint 😉) - and place a gate
3. Invite at least 1 sim to your lot, then either form a group (click on your sim, "actions", "form group") and select "go here with group" nside the compound - or go inside and select the "call over" interaction - either way, bring the visitor/ visitors inside the compound
4. Click on the gate, select "lock for everyone except household"
5. Leave the compound and wait - sometimes happens instantly, sometimes takes a few sim-hours, but someone will get bored and start to build the rocket for you!
6. Delete the fence and gate - or unlock the gate so the other sims can leave. You can then continue to build it, or if you leave them in there long enough, they'll fully build it 😁
Works every time (although really, we shouldn't need to do things like this to "fix" EAs bugs!!)