'There are known knowns. There are things we know that we know. There are known unknowns. That is to say, there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know. And then there is the future of Nama."

This statement was made by former US defence secretary Donald Rumsfeld in 2002. Well, he said it all except the bit about Nama.

At the time Rumsfeld made his "known unknown" speech, Ireland was looking towards the 2002 general election and then taoiseach Bertie Ahern was telling us that Fianna Fáil had "a lot done" and "more to do" for the country.

There was still room for more hot air in the property bubble and the idea that the country would ever need a state asset management agency was unthinkable. Ireland was awash with money and it was more conceivable that we would set up our own version of Nasa than ever need Nama.

Fast forward seven years. The bubble has burst and Nama has been set up to clear the debris. The government has taken a massive gamble and the future is scary.

One of the only 'known knowns' is that the future and predicted life span of Nama is completely unknown.

"All options are unpalatable. Nama is the least worst of the options available." That is how Green party chairman Dan Boyle described the government's 'bad-bank' plan after draft Nama legislation was published on Thursday.

Sinn Féin's Arthur Morgan was less diffident and claimed the government is committing "the crime of the century" by setting up Nama. Morgan was probably a bit premature with his 21st century 'Top of the Crime Pops' prediction but he is correct on one thing. Last week was historic.

The setting up of Nama is as important to the history of this state as our accession to the then EEC in 1973 or remaining neutral during the Second World War. It is a landmark, and the government's multi-billion-euro 'gamble' will be debated for many years. In reality, Boyle's view that Nama is the "least worst" of the available options may not be too wide of the mark.

Whether we like it or not, the consensus among the government's advisers including the Central Bank, the Financial Regulator and the National Treasury Management Agency, is that an asset management agency is the best means of stabilising the financial system, protecting depositors and ensuring the banks start lending money again.

In recent weeks, Frank Feighan, Fine Gael TD for Roscommon, was asked to leave the Dáil chamber by Ceann Comhairle John O'Donoghue after an angry outburst about the fact that small businesses were not getting access to credit from the banks.

The situation has changed little since Feighan's outburst: we now have 'zombie banks' that are not lending money into the economy. The government's primary motive in setting up Nama is to take possession of the banks' toxic loans and get money flowing again in an economy that has been paralysed.

So if the best advice available to the government has been to set up Nama and if it is the "least worst" option, what happens next? Nama has been conceived, so how will it develop after its birth this autumn? And most importantly, what is the life expectancy of this new creature?

In his poem 'Easter 1916', WB Yeats wrote about how Ireland had "changed, changed utterly" and "A terrible beauty is born". The economy has utterly changed in the past year and a 'terrible beauty' or monster has been born in the shape of Nama.

Now that the draft legislation has been published, the next step involves TDs, senators, interest groups and the general public (the biggest interest group in this instance) considering the draft legislation over the next six weeks.

The Construction Industry Federation (CIF) is just one of the bodies that has begun consulting its members on their views on Nama.

Finance minister Brian Lenihan has asked the opposition parties to digest the legislation and use the next six weeks to come up with any constructive amendments they feel should be made when the bill goes before the Dáil on 16 September.

Lenihan has come a long way in the past six months; after an extremely shaky start, he appears to be on top of his finance brief. His media performances in recent days have been strong and he has the appearance of a politician who is willing to take ideas about Nama on board.

Speaking on RTE's Morning Ireland on Friday, Siptu general secretary Jack O'Connor criticised the draft legislation for stipulating that Nama will have to account for itself in front of a Dáil committee only once a year. Lenihan later appeared on the same programme, and when O'Connor's criticism was put to him, Lenihan astutely poured cold water on it and said he would be willing to take O'Connor's suggestion on board.

Under the terms of last week's draft bill, Nama will be given extensive powers to acquire development loans from banks at a significant discount.

Lenihan has insisted the new agency will not be paying "bubble property prices" to the banks for the loans. This is crux of the Nama project. But how much will it cost? How exposed is Joe Public?

The process of valuing toxic assets has already begun, and the overall figure will be announced by Lenihan in the Dáil on 16 September.

"We are working on the valuation of these properties," Lenihan said on Friday. "We are continuing to do that work and I will announce, on behalf of the government, the approximate estimated figure for how much state bonds will be required to be issued in the Dáil in September. This is a very substantial exercise on behalf of the state to the taxpayer and the greatest of care must be taken in arriving at a final figure."

Nama's valuations will be based on the current market value of the asset, adjusted to reflect a longer-term economic value which the underlying asset could reasonably be expected to attain in a post-bubble market.

A key part of Nama's valuation process is that loans will be valued separately, and the actual amount of the 'haircut' – or discount – applied will depend on the quality of the property.

Details of the regulations governing the way the long-term economic value will be calculated are being drawn up by the minister at the moment.

The government will debate the first stage of the Nama bill from that date onwards and it is Lenihan's hope that the bill will get to committee stage in September.

With the second Lisbon treaty referendum looming on 2 October, it is expected that the bill will be parked for that campaign. It could become law in October, although it would be imprudent to pre-judge how the bill will proceed through Leinster House.

In the coming months, focus will shift to issues such as identifying suitable board members, and the make-up of the Nama board will be finalised. It will also hire around 50 staff.

Nama is expected to take over up to €90bn in risky loans but as the current value of these loans is far less, Nama will pay below this figure.

It will start by taking control of the loans of top 50 property developers, who have loans of €30bn, by Christmas. The agency will take on €22bn of loans for properties in Britain; as many of these are in London, it will expect to recoup money during the recovery in the London property market ahead of the 2012 Olympic Games in the city. Nama plans to buy the remaining €40bn of smaller loans advanced to 1,400 borrowers by next June.

Lenihan admitted that it could take 30 years for Nama to sort out toxic bank assets but he did say he expects most of its work to be done in between seven and 10 years. That is the best-case scenario.

This November, as Nama is born, it will be exactly 25 years since Business & Finance magazine carried the headline 'The Can of Worms at ICI'. A few months later, the Insurance Corporation of Ireland (ICI), a subsidiary of AIB, collapsed with losses of over £200m as a result of severe under-reserving and poor underwriting at its London office. Lenihan acknowledged last week that the loose ends of the ICI debacle are still being tied up. Nama is a much bigger monster and it is impossible to predict when its work will be done.

Morgan Kelly, economics professor at UCD, described the worst-case scenario for Nama in a recent article in the Irish Times. Labelling Nama "Fianna Fáil's shrine to the property bubble for which the party still yearns", Kelly's article was scathing of the project.

"Underlying Nama is the delusion that the collapse of our property bubble is a temporary downturn," he wrote. "In a few years' time, when the global economy recovers, we will be back building houses like it was 2006. All the ghost estates, empty office blocks, guestless hotels and weed-choked fields that Nama has bought on our behalf will once again be worth a fortune.

"The reality is that... empty apartment blocks in Dublin will eventually be rented, albeit at rates so low that many will decay into slums. However, most of the unfinished estates that litter rural Ireland – where the only economic activity was building houses – will never be occupied."

One of the most stark assessments of the Nama project came from Trinity College economist Constantin Gurdgiev on Friday.

"We are being sold a product we cannot see, in a quantity unknown to us, for a price we cannot access, with no deeds on this product passed to us," he wrote.

Not everyone is as sceptical about Nama but there is one 'known'. That 'known' is the fact that Nama's future is littered with unknowns.