Ospreys require a victory to give the club any chance of acquiring a seat at Europe's top table next season - even then it may still not be enough.
The Welshmen have won their last three matches, all with maximum points, since their home defeat to Scarlets at the end of March.
Alun Wyn Jones and Justin Tipuric headline an injury list of 14 potential first-team players but Tandy remains bullish about his side's chances.
"There's a really positive mood in the camp this week," he said.
"We realise the size of the challenge ahead, going up against a very good Ulster side who need the win for a play-off spot but we know that if we can go again and deliver another positive performance that we could get our own reward and it's really exciting.
"To bounce back like we have these last three games with a young squad and a full team of experienced, senior guys missing speaks volumes for the character of this squad.
"The desire and application of a team that has an average age of 23, 24, is outstanding and they've shown what being an Osprey is all about in recent weeks as they've grown on and off the field.
"We need more of that this week now, we want the boys to be relentless, to know their roles and to be clinical. If we can hit the right standards across the park then we have a chance of doing what we need to, then it'll be a case of what happens elsewhere.
"There'll be no throwing the towel in, we know from bitter experience in Europe this season that anything can happen on that last day, so we have to keep going."
A maximum point win would guarantee Ulster a Play-Off spot, and also give them any outside chance of that game being in Belfast.
Anything less and they will be looking at other results to confirm their place in the last four for a fourth successive year. The Ulstermen's only defeat in the last five rounds of Guinness PRO12 play was at Glasgow in round 18.
Ulster have lost just one of their last five fixtures against Ospreys: 20-31 at Liberty Stadium in the equivalent fixture in round 10 last season.
Director of Rugby, Les Kiss, has named his match day squad for the Guinness PRO12 Round 22 clash against Ospreys, with Craig Gilroy, a late withdrawal from the team last week, reinstated to the starting XV, which is otherwise unchanged from the 30-6 win over Leinster.
"I'd be lying if I said I didn't feel that expectation to get it done or believed that it can be done. To say anything less, I'd be underselling the ambition of what Ulster is and the ambition of the players," said Kiss.
"Especially the players that have got two or three years left of their opportunity here. I didn't want to come here and say, 'give me two or three years to do something', I wanted to come in and say, 'let's try and get in front of things as quick as we can and see if we can get there'."
At Liberty Stadium, 3pm
Referee: Marius Mitrea (FIR, 52nd competition game)
Assistant Referees: TBC
Citing Commissioner: Dennis Jones (WRU)
TMO: TBC
Live on Sky Sports and BBC NI
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland














